Integrated circuit with a laterally diffused metal oxide semiconductor device and method of forming the same

ABSTRACT

An integrated circuit with a transistor advantageously embodied in a laterally diffused metal oxide semiconductor device having a gate located over a channel region recessed into a semiconductor substrate and a method of forming the same. In one embodiment, the transistor includes a source/drain including a lightly or heavily doped region adjacent the channel region, and an oppositely doped well extending under the channel region and a portion of the lightly or heavily doped region of the source/drain. The transistor also includes a channel extension, within the oppositely doped well, under the channel region and extending under a portion of the lightly or heavily doped region of the source/drain.

This application is a continuation in part of, and claims priority to,U.S. patent application Ser. No. 11/805,233, entitled “LaterallyDiffused Metal Oxide Semiconductor Device and Method of Forming theSame,” filed on May 22, 2007, now, U.S. Pat. No. 7,759,184, issued Jul.20, 2010, which is a divisional of U.S. patent application Ser. No.10/767,684, entitled “Laterally Diffused Metal Oxide SemiconductorDevice and Method of Forming the Same,” filed on Jan. 29, 2004, now,U.S. Pat. No. 7,230,302, issued Jun. 12, 2007, all of which areincorporated herein by reference.

TECHNICAL FIELD

The present invention is directed, in general, to integrated circuitsand, more specifically, to an integrated circuit with a laterallydiffused metal oxide semiconductor device and method of forming thesame.

BACKGROUND

The design of early integrated circuits focused on implementing anincreasing number of small semiconductor devices on a semiconductorsubstrate to achieve substantial improvements in manufacturingefficiency and cost, product size, and performance. The continuingimprovements in the design of integrated circuits over the past fewdecades has been so dramatic and so pervasive in numerous products thatthe effects can be measured in changes in industries.

The design and construction of integrated circuits has continued toevolve in a number of different areas. One area of innovation is acontinuing reduction of feature sizes of semiconductor devices such ascontrol and signal processing devices formed on a semiconductorsubstrate. Another area of innovation is the advent of constructiontechniques to incorporate higher voltage semiconductor devices (alsoreferred to as “higher voltage devices”) having higher voltage handlingcapability such as switches of a power train of a power converter intothe integrated circuits.

An objective of incorporating control and signal processing devices on asemiconductor substrate with the higher voltage devices often encountersconflicting design requirements. More specifically, lower voltages(e.g., 2.5 volts (“V”)) are employed with the control and signalprocessing devices (hence, also referred to as “low voltage devices”) toprevent breakdown between the fine line structures thereof. A potentialdifference of only a few volts separated by a fraction of a micrometer(“μm”) can produce electric fields of sufficient magnitude to inducelocally destructive ionization in the control and signal processingdevices.

When employing the higher voltage devices on the same integrated circuittherewith, it is often necessary to sense and switch higher externalcircuit voltages (e.g., at least ten volts) on the integrated circuit.To accommodate the higher voltage devices on a semiconductor substratewith the control and signal processing devices, a large number ofprocessing steps are performed to produce the integrated circuit. Sincethe cost of an integrated circuit is roughly proportional to the numberof processing steps to construct the same, there has been limitedprogress in the introduction of low cost integrated circuits thatinclude both control and signal processing devices and higher voltagedevices such as the switches of the power train of a power converter.

The aforementioned constraints have been exacerbated by the need toemploy a substantial area of the semiconductor substrate to incorporatemore efficient and even higher voltage devices into an integratedcircuit. Inasmuch as the cost of a die that incorporates the integratedcircuit is roughly proportional to the area thereof, the presence of thehigher voltage devices conflicts with the reduction in area achieved byincorporating the fine line features in the control and signalprocessing devices.

With respect to the type of semiconductor devices readily available,complementary metal oxide semiconductor (“CMOS”) devices are commonlyused in integrated circuits. The CMOS devices such as P-type metal oxidesemiconductor (“PMOS”) devices and N-type metal oxide semiconductor(“NMOS”) devices are used as logic devices, memory devices, or otherdevices such as the control and signal processing devices. In additionto the CMOS devices, laterally diffused metal oxide semiconductor(“LDMOS”) devices such as P-type laterally diffused metal oxidesemiconductor (“P-LDMOS”) devices and N-type laterally diffused metaloxide semiconductor (“N-LDMOS”) devices are also commonly used inintegrated circuits. LDMOS devices are generally used for the highervoltage devices in the integrated circuit. In the context of CMOStechnology, the higher voltage devices generally relate to devices thatoperate at voltages above a standard operating voltage for the selectedCMOS devices (e.g., the low voltage devices). For instance, CMOS devicesemploying fine line structures having 0.25 micrometer line widthsoperate at or below about 2.5 volts. Thus, higher voltage devicesgenerally include any devices operating above approximately 2.5 volts.

Integrating the CMOS and LDMOS devices on a semiconductor substrate hasbeen a continuing goal in the field of microelectronics and has been thesubject of many references over the years. For instance, U.S. Pat. No.6,541,819 entitled “Semiconductor Device Having Non-Power Enhanced andPower Enhanced Metal Oxide Semiconductor Devices and a Method ofManufacture Therefor,” to Lotfi, et al., issued Apr. 1, 2003, which isincorporated herein by reference, incorporates non-power enhanced metaloxide semiconductor devices (i.e., low voltage devices) with powerenhanced metal oxide semiconductor devices (i.e., higher voltagedevices) on a semiconductor substrate. While Lotfi, et al. provides aviable alternative to integrating low voltage devices and higher voltagedevices on the semiconductor substrate, further improvements arepreferable in view of the higher voltage handling capability associatedwith the use of higher voltage devices such as with the LDMOS devices inthe power train of a power converter.

In the field of power microelectronics, the CMOS devices may be employedas the control and signal processing devices integral to the controllerof a power converter. As an example, the control and signal processingdevices are employed as low voltage switches and comparators that formportions of the controller of the power converter. The LDMOS devices, onthe other hand, may be employed as the higher voltage devices integralto the power train of the power converter. The higher voltage devicesperform the power switching functions to control the flow of power to,for instance, a microprocessor. The power switches include the mainpower switches, synchronous rectifiers, and other power switches germaneto the power train of the power converter. The power switches can alsobe used for circuit protection functions such as a rapidly actingelectronic version of an ordinary fuse or circuit breaker. Variations ofpower switches include metal oxide semiconductor field effecttransistors (“MOSFETs”) that exhibit low level gate-to-source voltagelimits (e.g. 2.5 volts) and otherwise are capable of handling the highervoltages germane to the power train of the power converter.

To achieve the overall reduction in size, the integrated circuits asdescribed herein should include control and signal processing deviceswith fine line structures having sub-micron line widths (e.g., 0.25micrometers) on a semiconductor substrate that operate with lowervoltages to prevent breakdown within the integrated circuit. At the sametime, the integrated circuit may incorporate higher voltage devices thatcan conduct amperes of current and withstand voltages of, for instance,at least ten volts. A benefit of incorporating the low voltage devicesand the higher voltage devices on the semiconductor substrate is that itis possible to accommodate higher switching frequencies in the design ofthe power processing circuit due to a reduction of parasiticcapacitances and inductances in the integrated circuit.

While a design and implementation of low voltage devices such as logicdevices that form portions of a microprocessor have been readilyincorporated into integrated circuits, the systems that power the logicdevices have not to date been readily incorporated into integratedcircuits. There has been pressure directed to the power electronicsindustry to make parallel improvements in the power conversiontechnology and, in particular, with the power converters that regulatethe power to, for instance, the microprocessors that employ a high levelof integrated circuit technology in the design thereof. Thus, anevolutionary direction in the power electronics industry is to reducethe size and cost of the power converters, which correspondingly inducesgreater levels of silicon integration in a design of the integratedcircuits embodying the same.

Although power converters have shown dramatic improvements in size,cost, and efficiency over the past few decades, the design of the powerconverters have not kept pace with the improvements in integratedcircuit technology directed to the logic devices and the like, whichfollow Moore's Law demonstrating a doubling of device (e.g., transistor)density about every 18 months. As representative examples ofimprovements in the smaller and more compact power converters, see U.S.Pat. No. 5,469,334, entitled “Plastic Quad-packaged Switched-modeIntegrated Circuit with Integrated Transformer Windings and Moldings forTransformer Core Pieces,” to Balakrishnan, issued on Nov. 21, 1995, andU.S. Pat. No. 5,285,369, entitled “Switched Mode Power Supply IntegratedCircuit with Start-up Self-biasing,” to Balakrishnan, issued on Feb. 8,1994, which are incorporated herein by reference. While Balakrishnan andother references have demonstrated noticeable improvements ofincorporating power converters into an integrated circuit, an industrywide integration of higher voltage level devices (again, such as theswitches of the power train) into the design of integrated circuits,especially in power converters, has not yet gained industry wideadoption.

Another issue in a design of the power converters is an increase of theswitching frequency (e.g., five megahertz) of the power train thereof.The energy stored in reactive circuit elements (e.g., inductors andcapacitors) associated with the power converter is inverselyproportional to the switching frequency, and the size of the reactivecircuit elements is also correspondingly inversely proportional to theswitching frequency. A power converter is generally designed to switchat a frequency that does not compromise power conversion efficiency.Otherwise, the switching frequency could be simply increased with aconsequent reduction in the size and cost of the power converter.Achieving a high switching frequency is dependent on reducing theparasitic circuit elements such as stray interconnection capacitance andinductance. As mentioned above, incorporating the low voltage devicesand the higher voltage devices within an integrated circuit embodyingthe power converter can have a significant impact in reducing theinterconnection paths and consequently the stray interconnectionparasitic capacitance and inductance. Additionally, reducing theinherent parasitic losses in the switches of the power converter such asenergy stored in a gate of a MOSFET can also have a significant impacton the switching frequency of the power converter.

Accordingly, what is needed in the art is an integrated circuit,semiconductor device and method of forming the same that incorporateslow voltage devices and higher voltage devices on a semiconductorsubstrate that overcomes the deficiencies in the prior art.Additionally, there is a need in the art for a higher voltage device(e.g., a transistor such as a LDMOS device) that can accommodate highervoltages without excessive on-state resistance, and is capable of beingintegrated with low voltage devices on a semiconductor substrate in anintegrated circuit that may form a power converter or portions thereof.

SUMMARY OF THE INVENTION

These and other problems are generally solved or circumvented, andtechnical advantages are generally achieved, by advantageous embodimentsof the present invention, which includes an integrated circuit formed ona semiconductor substrate and configured to accommodate higher voltagedevices and low voltage devices therein. In one embodiment, theintegrated circuit includes a transistor advantageously embodied in alaterally diffused metal oxide semiconductor (“LDMOS”) device having agate located over a channel region recessed into a semiconductorsubstrate. The transistor also includes a source/drain including alightly or heavily doped region adjacent the channel region, and anoppositely doped well extending under the channel region and a portionof the lightly or heavily doped region of the source/drain. Thetransistor still further includes a channel extension, within theoppositely doped well, under the channel region and extending under aportion of the lightly or heavily doped region of the source/drain. Thetransistor may be embodied in a semiconductor device with acomplementary metal oxide semiconductor (“CMOS”) device formed on thesemiconductor substrate. The transistor may also form a driver switch ofan integrated circuit. The integrated circuit may be employable with apower converter and the transistor operates as a power switch of a powertrain thereof or as a driver switch of a driver configured to provide adrive signal to the power switch of the power converter.

The foregoing has outlined rather broadly the features and technicaladvantages of the present invention in order that the detaileddescription of the invention that follows may be better understood.Additional features and advantages of the invention will be describedhereinafter which form the subject of the claims of the invention. Itshould be appreciated by those skilled in the art that the conceptionand specific embodiment disclosed may be readily utilized as a basis formodifying or designing other structures or processes for carrying outthe same purposes of the present invention. It should also be realizedby those skilled in the art that such equivalent constructions do notdepart from the spirit and scope of the invention as set forth in theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, reference isnow made to the following descriptions taken in conjunction with theaccompanying drawings, in which:

FIG. 1 illustrates a diagram of an embodiment of a power converterembodied in, or portions thereof, an integrated circuit constructedaccording to the principles of the present invention;

FIG. 2 illustrates a schematic diagram of an embodiment of a controllerin an environment of a power converter embodied in, or portions thereof,an integrated circuit constructed according to the principles of thepresent invention;

FIG. 3 illustrates a schematic diagram of an embodiment of a driver of apower converter embodied in, or portions thereof, an integrated circuitconstructed according to the principles of the present invention;

FIGS. 4 through 17 illustrate cross-sectional views of an embodiment ofconstructing a semiconductor device embodied in, or portions thereof, anintegrated circuit according to the principles of the present invention;

FIG. 18 illustrates a cross-sectional view of another embodiment of asemiconductor device embodied in, or portions thereof, an integratedcircuit constructed according to the principles of the presentinvention;

FIG. 19 illustrates a cross-sectional view of an embodiment of amicromagnetic device employable in an integrated circuit constructedaccording to the principles of the present invention;

FIG. 20 illustrates a partial cross-sectional view of an embodiment ofmagnetic core layers of a magnetic core of a micromagnetic deviceemployable in an integrated circuit constructed according to theprinciples of the present invention; and

FIG. 21 illustrates a cross-sectional view of an embodiment of an outputfilter employable in an integrated circuit constructed according to theprinciples of the present invention.

Corresponding numerals and symbols in the different figures generallyrefer to corresponding parts unless otherwise indicated. The figures aredrawn to clearly illustrate the relevant aspects of the preferredembodiments and are not necessarily drawn to scale.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the presently preferred embodiments arediscussed in detail below. It should be appreciated, however, that thepresent invention provides many applicable inventive concepts that canbe embodied in a wide variety of specific contexts. The specificembodiments discussed are merely illustrative of specific ways to makeand use the invention, and do not limit the scope of the invention.

The present invention will be described with respect to preferredembodiments in a specific context, namely, an integrated circuitincluding a transistor [e.g., embodied in a laterally diffused metaloxide semiconductor (“LDMOS”) device] and methods of forming the same.While the principles of the present invention will be described in theenvironment of a power converter, any application that may benefit froma transistor that can accommodate higher voltages and is integrable witha low voltage device [e.g., complementary metal oxide semiconductor(“CMOS”) device] on a semiconductor substrate is well within the broadscope of the present invention.

The advantages associated with incorporating the higher voltage LDMOSdevices with the low voltage CMOS devices facilitate the ongoingincorporation of integrated circuits with higher levels of integrationinto more products such as power converters. For the purposes of thepresent invention, higher voltage devices refer to devices that canaccommodate higher operating voltages than the standard operatingvoltages for a referenced low voltage device. As an example and in thecontext of CMOS technology, the higher voltage devices generally relateto devices that operate at voltages above a standard operating voltagefor the selected CMOS devices (e.g., the low voltage devices). Forinstance, CMOS devices employing fine line structures having 0.25micrometer line widths operate at or below about 2.5 volts. Thus, highervoltage devices generally include any devices operating aboveapproximately 2.5 volts. In yet another context, the higher voltagedevices also generally include devices that may exhibit a low levelgate-to-source voltage limit (e.g., 2.5 volts) and, at the same time,can handle drain-to-source voltages above the gate-to-source voltagelimit thereof (e.g., at least ten volts).

An area of ongoing development of semiconductor devices is obtaining ahigher operating voltage for a transistor for a given semiconductorfeature size without the need to produce a semiconductor chip withsubstantial active area. A number of processes and techniques have beendeveloped to increase a drain breakdown voltage of an LDMOS. Oneprocess, a reduced surface field (“RESURF”) process, increases the drainbreakdown voltage by reducing a peak electric field between the drainand the gate or between the drain and the source. A general overview ofthe RESURF process is provided by A. Ludikhuize, in the paper entitled“A Review of RESURF Technology,” Proceedings of IEEE ISPSD 2000, May 22,2000, pp. 11-18, which is incorporated herein by reference. The LDMOSdesigns employing RESURF, however, often suffer from hot carrierinjection (“HCI”), which may degrade the crystal structure of the deviceover time and thereby limit its long term reliability.

Another process to increase a drain breakdown voltage in an LDMOS,particularly for a short gate with a thin gate oxide, is the use of anextended drain structure. To form an extended drain structure, animplant is formed in a drain area with a tailored shape and dopingdensity to raise the device breakdown voltage. As drain voltagescontinue to be increased in new designs (e.g., at least ten volts),however, an extended drain structure that can withstand the higher drainvoltages does not provide a sufficiently low device on-state resistanceto meet market challenges for new applications. The extended drainstructure inherently increases the on-state resistance of the device,resulting in reduced efficiency of a power converter or other productemploying the semiconductor device.

A further structure developed to provide increased drain voltage in anLDMOS is described by Bude, et al. (“Bude”) in U.S. Pat. No. 7,262,476entitled “Semiconductor Device Having Improved Power Density,” issuedAug. 28, 2008, which is incorporated herein by reference. Bude describesa deep pocket implant in a drain region that reduces the device'smaximum electric field strength. The deep pocket implant described byBude, which must be located at a significant distance below a lightlydoped drain (“LDD”), reduces hot carrier injection, but it alsointroduces alignment constraints for construction of the structure aswell as substantial implementation expense.

As introduced herein, an implant is formed, preferably employing an ionimplantation process, during an early stage of a die manufacturingprocess to produce a channel extension that enables a substantialreduction in drain length as well as a reduction of the distance betweenthe gate and the drain. Formation of the implant may save as much as,without limitation, 30% of the active device area to achieve aparticular transistor on-state resistance. The implant may be placed ata reasonable depth under a portion of a lightly doped region of thedrain of the device (e.g., LDMOS device).

The channel extension may be a implant of the same doping type (i.e.,N-doped or P-doped) as the channel region, and is located thereunderwith a particular channel extension length. The doping specie such asboron, phosphorus, etc., may be different than the doping specie of thechannel region. The channel extension produces a more conformal profileof the electric field in the channel and drain regions to reduce a peakelectric field. By reducing the peak electric field, the length of aconventional LDD implant region does not need to be increased towithstand a high breakdown voltage, thereby reducing the on-stateresistance for a given breakdown voltage. The choice of the channelextension dimensions (length and depth) and doping levels are selectedto meet a breakdown voltage and resistance objective.

The implant to form the channel extension avoids alignment constraintsintroduced by Bude, and may be formed with two additional masking levelswith little complexity and with associated cost savings. The channelextension does not require precise alignment to the gate. Accordingly,the implant step to form the channel extension can be done in a lesscontrolled, less precise manner. Thus, the channel extension is moreforgiving in terms of feature size control, and is simpler to form thanthe pocket of Bude. It fits well into the existing CMOS process flow,and can be fabricated in the presence of a background core complementaryoxide semiconductor (“COS”) process into which it fits in a modularfashion.

Forming an implant in an existing manufacturing process is an importantconsideration for low-cost compatibility with CMOS processes and withhigh levels of integration employable in applications such as advancedpower management systems. In general, there is a set of process-relatedconditions for implants, diffusions, thermal cycles, etc., that are usedin the construction of an integrated circuit and have a direct bearingon the restructuring of the extended drain. The objective is to stayreasonably compatible and consistent with these process-relatedconditions so as not to substantially change or increase the cost of thecore CMOS processes.

The implant that forms the channel extension enables trade-offsnecessary and/or desirable when the key parts of a core manufacturingprocess to produce a lightly doped drain well and drain dimensions, etc.are modified to accommodate a channel implement extension (“CIE”) thatresults in improved transistor power density performance. The technologyis selected around a power management set of transistor performanceparameters. These transistor performance parameters include on-stateresistance, parasitic capacitances, and switching times (turn-on andturn-off) from full current and voltage to zero current and voltage.Parameters that characterize the design of the channel extension includechannel extension length, dose per square centimeter (“cm”) to form thesame and energy. A further parameter that characterizes the design ofthe channel extension is the dose applied to the semiconductor device toform the lightly doped drain.

Referring initially to FIG. 1, illustrated is a diagram of an embodimentof a power converter embodied in, or portions thereof, an integratedcircuit constructed according to the principles of the presentinvention. The power converter includes a power train 110, a controller120 and a driver 130, and provides power to a system such as amicroprocessor. While in the illustrated embodiment, the power train 110employs a buck converter topology, those skilled in the art shouldunderstand that other converter topologies such as a forward convertertopology are well within the broad scope of the present invention.

The power train 110 of the power converter receives an input voltageV_(in) from a source of electrical power (represented by a battery) atan input thereof and provides a regulated output voltage V_(out) topower, for instance, a microprocessor at an output of the powerconverter. In keeping with the principles of a buck converter topology,the output voltage V_(out) is generally less than the input voltageV_(in) such that a switching operation of the power converter canregulate the output voltage V_(out). A main switch Q_(mn) [e.g., aP-channel metal oxide semiconductor field effect transistor (“MOSFET”)embodied in a P-type laterally diffused metal oxide semiconductor(“P-LDMOS”) device] is enabled to conduct for a primary interval(generally co-existent with a primary duty cycle “D” of the main switchQ_(mn)) and couples the input voltage V_(in) to an output filterinductor L_(out). During the primary interval, an inductor currentI_(Lout) flowing through the output filter inductor L_(out) increases ascurrent flows from the input to the output of the power train 110. An ACcomponent of the inductor current I_(Lout) is filtered by the outputcapacitor C_(out).

During a complementary interval (generally co-existent with acomplementary duty cycle “1-D” of the main switch Q_(mn)), the mainswitch Q_(mn) is transitioned to a non-conducting state and an auxiliaryswitch Q_(aux) [e.g., a N-channel MOSFET embodied in a N-type laterallydiffused metal oxide semiconductor (“N-LDMOS”) device] is enabled toconduct. The auxiliary switch Q_(aux) provides a path to maintain acontinuity of the inductor current I_(Lout) flowing through the outputfilter inductor L_(out). During the complementary interval, the inductorcurrent I_(Lout) through the output filter inductor L_(out) decreases.In general, the duty cycle of the main and auxiliary switches Q_(mn),Q_(aux) may be adjusted to maintain a regulation of the output voltageV_(out) of the power converter. Those skilled in the art shouldunderstand, however, that the conduction periods for the main andauxiliary switches Q_(mn), Q_(aux) may be separated by a small timeinterval to avoid cross conduction therebetween and beneficially toreduce the switching losses associated with the power converter.

The controller 120 of the power converter receives a desiredcharacteristic such as a desired system voltage V_(system) from aninternal or external source associated with the microprocessor, and theoutput voltage V_(out) of the power converter. The controller 120 isalso coupled to the input voltage V_(in) of the power converter and areturn lead of the source of electrical power (again, represented by abattery) to provide a ground connection therefor. While only a singleground connection is illustrated in the present embodiment, thoseskilled in the art should understand that multiple ground connectionsmay be employed for use within the controller 120. A decouplingcapacitor C_(dec) is coupled to the path from the input voltage V_(in)to the controller 120. The decoupling capacitor C_(dec) is configured toabsorb high frequency noise signals associated with the source ofelectrical power to protect the controller 120.

In accordance with the aforementioned characteristics, the controller120 provides a signal (e.g., a pulse width modulated signal S_(PWM)) tocontrol a duty cycle and a frequency of the main and auxiliary switchesQ_(mn), Q_(aux) of the power train 110 to regulate the output voltageV_(out) thereof. The controller 120 may also provide a complement of thesignal (e.g., a complementary pulse width modulated signal S_(1-PWM)) inaccordance with the aforementioned characteristics. Any controlleradapted to control at least one switch of the power converter is wellwithin the broad scope of the present invention. As an example, acontroller employing digital circuitry is disclosed in U.S. Pat. No.7,038,438, entitled “Controller for a Power Converter and a Method ofControlling a Switch Thereof,” to Dwarakanath, et al., issued May 2,2006, and U.S. Pat. No. 7,019,505, entitled “Digital Controller for aPower Converter Employing Selectable Phases of a Clock Signal,” toDwarakanath, et al, issued Mar. 28, 2006, which are incorporated hereinby reference.

The power converter also includes the driver 130 configured to providedrive signals S_(DRV1), S_(DRV2) to the main and auxiliary switchesQ_(mn), Q_(aux), respectively, based on the signals S_(PWM), S_(1-PWM)provided by the controller 120. There are a number of viablealternatives to implement a driver 130 that include techniques toprovide sufficient signal delays to prevent crosscurrents whencontrolling multiple switches in the power converter. The driver 130typically includes switching circuitry incorporating a plurality ofdriver switches that cooperate to provide the drive signals S_(DRV1),S_(DRV2) to the main and auxiliary switches Q_(mn), Q_(aux). Of course,any driver 130 capable of providing the drive signals S_(DRV1), S_(DRV2)to control a switch is well within the broad scope of the presentinvention.

According to the principles of the present invention, the main andauxiliary switches Q_(mn), Q_(aux) are power switches that can beincorporated into a semiconductor device in an integrated circuitproximate control or signal processing devices that perform many of thecontrol functions of the controller 120 of the power converter. Asmentioned above, the control and signal processing devices are typicallyCMOS devices such as P-type metal oxide semiconductor (“PMOS”) devicesand N-type metal oxide semiconductor (“NMOS”) devices (also generallyreferred to as a “CMOS device and another CMOS device,” and vice-versa).The PMOS and NMOS devices may also be referred to as P-channel andN-channel MOSFETs, respectively. Lower voltages (e.g., 2.5 volts) areemployed with the control and signal processing devices (hence, alsoreferred to as “low voltage devices”) to prevent breakdown between thefine line structures thereof.

The main and auxiliary switches Q_(mn), Q_(aux) of the power train 110,selected switches or other devices within the controller 120, and onesof the plurality of driver switches of the driver 130 are typicallyformed by LDMOS devices that handle higher voltages (e.g., at least tenvolts) and hence are referred to as higher voltage devices. Integratingthe control and signal processing devices, power switches and otherswitches (e.g., the driver switches) on a semiconductor substrateprovides opportunities for substantial reductions in cost and size of anintegrated circuit employable with a power converter or other apparatusemploying like devices.

Additionally, when providing a drive signals S_(DRV1), S_(DRV2) to aswitch (e.g., the main switch Q_(mn)) such as a P-channel MOSFET havinga control voltage limit (i.e., a gate voltage limit) of 2.5 volts, andin the environment of a power converter having a nominal input voltageV_(in) of five volts, the extended voltage range present on the gateterminal of the main switch Q_(mn) may break down the integrity of thethin gate oxide thereof. In other words, when the input voltage V_(in)to the power converter, which is translated into the drive signalS_(DRV1) to the main switch Q_(mn) under certain conditions as describedabove exceeds the gate voltage limit thereof, the main switch Q_(mn) maybe damaged and fail. Another layer of complexity arises when theplurality of driver switches of the driver 130 are referenced to avoltage level (e.g., a ground potential) and the main switch Q_(mn) tobe driven is referenced to another voltage (e.g., the input voltageV_(in) to the power converter). Colloquially, the main switch Q_(mn) ofthe power converter is referred to as a “floating” switch. A driver 130for the power converter, therefore, should be capable of handlingapplications wherein the main switch Q_(mn) to be driven exhibits asmaller control voltage limit (e.g., gate voltage limit) from thecontrol terminal to another terminal (e.g., the gate terminal to thesource terminal) thereof and is referenced to a voltage level differentfrom the driver 130.

Turning now to FIG. 2, illustrated is a schematic diagram of anembodiment of a controller in an environment of a power converterembodied in, or portions thereof, an integrated circuit constructedaccording to the principles of the present invention. The powerconverter includes a controller 210, a driver 220 and a power train 230.The controller 210 provides a signal (e.g., a pulse width modulatedsignal S_(PWM)) to control a duty cycle and a frequency of main andauxiliary switches Q_(mn), Q_(aux) of the power train 230 to regulate anoutput characteristic (e.g., an output voltage V_(out)) thereof. Thecontroller 210 may also provide a complement of the signal (e.g., acomplementary pulse width modulated signal S_(1-PWM)) via a level shiftand crossover circuit 237. The level shift and crossover control circuit237 is also adapted to adjust a delay between the signals S_(PWM),S_(1-PWM) that control the duty cycle of the main and auxiliary switchesQ_(mn), Q_(aux) to substantially prevent a cross conduction and enhancethe switching transitions therebetween.

The power train 230 employs a buck converter topology, which has beendescribed above with respect to FIG. 1. The driver (e.g., a levelshifting gate driver) 220 provides gate drive signals S_(DRV1), S_(DRV2)for the main and auxiliary switches Q_(mn), Q_(aux), and also for asense switch (also referred to as a “switch in a controller 210 of thepower converter,” e.g., a P-channel MOSFET embodied in a P-LDMOS device,or also referred to as “another LDMOS device”) Q_(s). The sense switchQ_(s) is configured to measure an output characteristic (e.g., an outputcurrent) of the power converter.

The low voltage and higher voltage devices of the power converter may beembodied in a semiconductor device as illustrated and described withrespect to FIG. 4, et seq. to form portions of a power converterembodied in an integrated circuit. Additionally, ones of the devices ofthe power converter such as an output inductor L_(out) and outputcapacitor C_(out) of the power train 230, and a soft-start capacitorC_(ss) and a select resistor R_(select) (which selects a set point forthe output voltage V_(out)) associated with the controller 210 may bediscrete devices incorporated into or with an integrated package withthe semiconductor devices that embody other devices of the powerconverter and still remain within the broad scope of the presentinvention. The discrete devices are often employed with the powerconverter to provide application flexibility to allow for costreductions and design options in constructing the power converter.

The controller 210 is coupled to the input voltage V_(in) and the outputvoltage V_(out) of the power converter and to first and second groundconnections PGND, AGND. For a representative power converter, the inputvoltage V_(in) is unregulated and falls within an operational range of2.5 to 6.5 volts. The output voltage V_(out) is well regulated (e.g.,within a three percent tolerance) and can be adjusted between, forinstance, 1.2 to 3.5 volts. The controller 210 of the power converteralso receives a desired characteristic such as a desired system voltageV_(system) from an internal or external source associated with, forinstance, a microprocessor powered by the power converter.

A soft start operation of the power converter may be adjusted by aselection of a soft start capacitor C_(ss), and the output voltageV_(out) may be adjusted by the select resistor R_(select). A signalindicating a normal operation of the power converter is provided via apower good connection PWRGD. The active devices of the power converterare powered from the input voltage V_(in) or from an internal, regulatedvoltage source, configured as a linear regulator 235 coupled to theinput voltage V_(in). The linear regulator 235 can be implemented as adissipative regulator as hereinafter described.

As is well understood by those skilled in the art, the first and secondground connections PGND, AGND are representative of ground connectionsfor the higher voltage devices handling higher currents and the lowvoltage devices handling low currents, respectively. The first groundconnection PGND is for currents flowing in the higher voltage devicesthat are less sensitive to system noise. The second ground connectionAGND is for currents flowing in the low voltage devices that are moresensitive to system noise. The first and second ground connections PGND,AGND are typically coupled at a single point within the power converter.

As described herein and, more specifically, with respect to FIG. 4, etseq. below, the low voltage devices are generally embodied in PMOS andNMOS devices, which may be integrable with the higher voltage devices,embodied in P-LDMOS and N-LDMOS devices in a semiconductor device. As aresult, the power converter is more readily incorporated into anintegrated circuit. Additionally, bias voltages V_(bias) (which may beinternally or externally generated) are resident throughout thecontroller 210. The higher voltage devices within the power converteroperate from a higher voltage source such as the input voltage V_(in),and the low voltage devices operate from a low voltage source, which isusually well regulated such as the bias voltages V_(bias). The voltagesource connections within the power converter are not intended to beexhaustive, but rather indicative of possible operational voltages forthe particular devices of the power converter.

An exemplary operation of the controller 210 will hereinafter bedescribed. A switching frequency of the power train 230 is generated bya sawtooth generator 240, which may be implemented using a currentsource to charge a capacitor coupled to a comparator (not shown). Whenthe voltage of the capacitor exceeds a threshold value, the comparatorenables a switch (not shown), quickly discharging the capacitor. Thecharge and discharge process regularly repeats, generating a sawtoothwaveform for the voltage across the capacitor. To provide a consistentswitching frequency, the sawtooth generator 240 is generally poweredfrom an internal, regulated voltage source providing the bias voltageV_(bias). A trim resistor R_(trim) may be included to adjust theswitching frequency during the design and manufacture of the controller210. For a better understanding of sawtooth generators, see “The Art ofElectronics,” by Horowitz, et al., Cambridge University Press, SecondEdition, pp. 288-291, 1989, the entire reference being incorporatedherein by reference.

The output voltage V_(out) is coupled through a compensation network 245to a non-inverting input of an error amplifier 250 of the controller210. Alternatively, the voltage representing the output voltage V_(out)may be determined from a remote location in a distribution network andprovided to the error amplifier 250. The error amplifier 250 is furthercompensated by a feedback network represented by a compensationcapacitor C_(comp). More extensive compensation networks can be providedas necessary for the error amplifier 250 as the application dictates.The compensation network 245 is coupled, via a select connection SEL, tothe select resistor R_(select), which is coupled to the second groundconnection AGND. The select resistor R_(select) provides an option toselect the set point for the output voltage V_(out) for the powerconverter.

The output of the error amplifier 250 is coupled to the non-invertinginput of a comparator (e.g., a PWM comparator) 255 that compares theoutput of the error amplifier 250 with an output of the sawtoothgenerator 240. An output of the PWM comparator 255 is high during aprimary interval when the main switch Q_(mn) of the power train isconfigured to conduct. The output of the PWM comparator 255 is lowduring a complementary interval when the main switch Q_(mn) of the powertrain is transitioned to a non-conducting state and the auxiliary switchQ_(aux) is configured to conduct. A non-inverting input of the erroramplifier 250 is coupled to a bandgap reference circuit 260 thatsupplies a well-regulated voltage (e.g., 1.07 volts) and a referencevoltage selector 265. The reference voltage selector 265 provides areference voltage V_(ref) to the non-inverting input of the erroramplifier 250 to establish a reference comparison for regulating theoutput voltage V_(out) of the power converter.

The bandgap reference circuit 260 preferably uses bipolar CMOStechnology and includes a disable pin (not shown) to disable an outputtherefrom. For example, when the disable pin is pulled high, the outputfrom the bandgap reference circuit 260 can be pulled close to a groundpotential with a switch (not shown), thereby disabling an operation ofthe power converter. The compensation network 245, as indicated above,is coupled to the select resistor R_(select) to provide the set pointfor the output voltage V_(out). The select resistor R_(select) may becoupled and operative in parallel with a resistor in a voltage dividernetwork 247 to control a fraction of the output voltage V_(out) therebyfurther refining a set point for the output voltage V_(out) for thepower converter. The use of voltage dividers, in general, to alter setpoints is well understood in the art and will not herein be described.

A soft start operation of the power converter is controlled, in part, bya soft start capacitor C_(ss). During a start up period of the powerconverter, the output voltage V_(out) of the power converter issubstantially zero, whereas during normal operation, a control loop ofthe controller 210 controls the conduction periods of the main andauxiliary switches Q_(mn), Q_(aux) to provide a regulated output voltageV_(out). When the main switch Q_(mn) is initially enabled to conduct andthe auxiliary switch Q_(aux) is non-conducting, a substantial in-rushcurrent to the power converter may occur in accordance with the inputvoltage V_(in) to charge the output capacitor C_(out). This conditionmay produce a substantial overshoot of the output voltage V_(out) as theoutput inductor L_(out) and output capacitor C_(out) resonantly ring inresponse to the in-rush current.

Thus, a slowly increasing set point for the control loop during thestart up period is preferable and can be achieved by increasing avoltage across the soft start capacitor C_(ss) at a controlled rate.During an initial operation of the power converter (and/or during are-start operation), the soft start capacitor C_(ss) is charged by acurrent source 270 (via a soft start connection SS), which is coupled tothe reference voltage selector 265. The reference voltage selector 265compares a voltage across the soft start capacitor C_(ss) with a voltageprovided by the bandgap reference circuit 260 and the system voltageV_(system) and selects the smaller value therefrom. The resultingreference voltage V_(ref) from the reference voltage selector 265 isprovided to the non-inverting input of the error amplifier 250 toregulate the set point for the output voltage V_(out) for the powerconverter.

Thus, during the soft start operation and when the voltage across thesoft start capacitor C_(ss) is smaller than the voltage of the bandgapreference circuit 260, the voltage across the soft start capacitorC_(ss) controls and slowly ramps up according to the charging rate ofthe soft start capacitor C_(ss). When the voltage across the soft startcapacitor C_(ss) exceeds the voltage from the bandgap reference circuit260, the voltage from the bandgap reference circuit 260 provides thecontrolling signal for the reference voltage V_(ref) to the erroramplifier 250. As an example, the value of the soft start capacitorC_(ss) is 15 nanofarads and the current source 270 provides about 10microamperes of current. This combination results in a rate of increaseof the voltage across the soft start capacitor of about 0.67volts/millisecond. Inasmuch as an inverting input to a soft startcomparator 275 is about, for instance, 0.8 volts, a time delay of about1.2 milliseconds is sustained before a soft start AND gate 280 enables aswitching operation of the power train 230 of the power converter. Ofcourse, the period of delay can be altered by changing the value of thesoft start capacitor C_(ss) or the value of the current source 270.

The linear regulator 235 provides a well regulated, low voltage biasvoltage V_(bias) (e.g., 2.5 volts) to supply power for the low voltagedevices having voltage limitations as generally determined by fine linesemiconductor structures thereof. The linear regulator 235 is poweredfrom the input voltage V_(in) and is coupled to a bypass capacitorC_(bp). The bypass capacitor C_(bp) can be formed from a semiconductordevice as described herein or by other device techniques and structures.Additional bypass capacitors C_(bp) may be employed within thecontroller 210 and power converter, in general, to absorb system noisetherein.

The linear regulator 235 preferably includes a higher voltage deviceimplemented with an N-LDMOS device acting as a series-pass, regulatingswitch (not shown). An operational amplifier (not shown) is included inthe linear regulator 235 that senses the bias voltage V_(bias) and areference voltage V_(ref) such as provided by the bandgap referencecircuit 260 to provide negative feedback to a control terminal of theseries-pass, regulating switch, thereby providing voltage regulation forthe bias voltage V_(bias). The design of dissipative linear regulators235 with a feedback control are well known in the art and will notherein be described. For a better understanding of the design ofdissipative linear regulators 235, see chapter six of Horowitz, et al.

A number of circuits such as protection circuits within the controller210 disable an operation of the power converter during unusual orundesirable operating conditions. The output of the circuits arecombined via AND logic gates with an output from the PWM comparator 255to disable the operation of the power converter when necessary. Athermal shutdown circuit 282 monitors a temperature of the powerconverter (e.g., a temperature of the switch embodied in a semiconductordevice located on a semiconductor substrate) to protect, for example,against a possible low impedance circuit coupled inadvertently across anoutput of the power train 230. The temperature monitoring function canbe provided using a voltage reference (not shown), which is dependent,preferably linearly, on the temperature of the monitored portion of thepower converter. An output of the voltage reference is compared, forinstance, with the output of the bandgap reference circuit 260 using acomparator (not shown) and, when there is a sufficient voltagedifference therebetween, the comparator switches and provides a signalto a protection circuit AND gate 284.

The protection circuit AND gate 284 is also coupled to an under voltagelockout circuit 285 that compares the input voltage V_(in) to a limitingthreshold voltage and, when the input voltage V_(in) is less than thethreshold voltage, another signal is provided to the protection circuitAND gate 284. Thus, the output of the protection circuit AND gate 284provides an indication of either a high temperature condition or anunacceptably low input voltage V_(in) and disables the operation of thepower converter accordingly. For further protection during a faultcondition, when the main switch Q_(mn) is transitioned to anon-conducting state, the auxiliary switch Q_(aux) is enabled to conductby the action of the level shifting gate driver 220, thereby dischargingthe output capacitor C_(out) and providing further protection for theoutput voltage V_(out) of the power converter. As an example, the undervoltage lockout circuit 285 disables the operation of the powerconverter when the input voltage V_(in) is less than 2.5 volts. When theinput voltage V_(in) is less than about 2.6 volts, the linear regulator235 saturates “full on” and may lose its regulation capability, causinga drop in the bias voltage V_(bias). A sufficient voltage compliance,however, can be designed into the various devices in the power converterto enable proper operation when the bias voltage V_(bias) is slightlyless than the desired regulated value.

An output of the protection circuit AND gate 284 is also coupled to asoft start switch Q_(ss) through an inverter 287. The purpose of thesoft start switch Q_(ss) is to discharge the soft start capacitor C_(ss)whenever a temperature within the power converter exceeds a limit or theinput voltage V_(in) is below a safe operating point for the power train230. Discharging the soft start capacitor C_(ss) essentially sets theset point for the output voltage V_(out) for the power train 230 tozero. The soft start capacitor C_(ss) may also be discharged by acircuit external to the power converter, such as by an external switch,to disable an operation of the power converter based on external systemrequirements.

The protection circuit AND gate 284 provides an input to the soft startAND gate 280, which is also coupled to the soft start comparator 275.The soft start AND gate 280 monitors an output of the soft startcomparator 275, which is coupled to the soft start capacitor C_(ss). Thesoft start AND gate 280 is coupled to a PWM AND gate 253 and configuredto disable the power train 230 whenever a voltage across the soft startcapacitor C_(ss) is less than a threshold value. In the presentembodiment, the threshold value, coupled to inverting input of the softstart comparator 275, is preferably about 0.8 volts. The threshold valuemay be derived from the bandgap reference circuit 260. Thus, a softstart circuit of the controller 210 includes, among other things, thesoft start capacitor C_(ss), the soft start switch Q_(ss) and the softstart comparator 275.

The controller 210 also includes other protective circuits such as anover current protection circuit 290. A sense switch Q_(s) is coupled inparallel with the main switch Q_(mn) of the power train 230 and iscontrolled to conduct synchronously with the main switch Q_(mn). A senseresistor R_(s) is coupled in series with the sense switch Q_(s). Thus, acurrent that flows through the sense resistor R_(s) is a fraction of thecurrent flowing through the main switch Q_(mn) when the main switchQ_(mn) conducts. A voltage proportional to the sensed current isamplified by an operational amplifier (not shown) in the over currentprotection circuit 290 and compared to a threshold value. If thethreshold value of the current through the sense resistor R_(s) isexceeded, a disable signal is provided to the PWM AND gate 253. Thus,the over current protection circuit 290 can disable the operation of thepower train 230 whenever current through the main switch Q_(mn), whichalso generally flows through the output inductor L_(out), exceeds athreshold value.

A power good monitoring circuit 292 is coupled to the output of the softstart AND gate 280, and preferably provides a signal to the power goodconnection PWRGD of the power converter to provide an externalindication that the power converter is operating normally. In addition,the power good monitoring circuit 292 is also coupled to the referencevoltage V_(ref) from the reference voltage selector 265. When the outputof the reference voltage selector 265 is above a predetermined referencevoltage level and the output of the soft start AND gate 280 is high, theoutput of the power good monitoring circuit 292 is high to indicate anormal operation of the power converter. It should be understood thatcircuits that monitor internal voltages and the outputs of logic gatesare generally well known in the art. It should further be understoodthat circuits that monitor the operation of a power converter can beoptionally coupled to various operating points within the controller 210and the power train 230 of the power converter.

Thus, a power converter embodied in, or portions thereof, an integratedcircuit has been illustrated and described with respect to FIG. 2. Asdescribed above, the devices of the power converter may be constructedwith low voltage devices and higher voltage devices integrable in asemiconductor device using fine line processing. Thus, for reasons asstated below, not only can control and signal processing devices, buthigher voltage devices such as the switches of the driver and powertrain, can be integrated into a semiconductor device thereby furtherfacilitating the power converter incorporated into an integratedcircuit.

Turning now to FIG. 3, illustrated is a schematic diagram of anembodiment of a driver of a power converter embodied in, or portionsthereof, an integrated circuit constructed according to the principlesof the present invention. The driver is adapted to provide a drivesignal S_(DRV) to control a switch having a control voltage limit. Morespecifically and in the illustrated embodiment, the driver is a gatedriver that provides a gate drive signal S_(DRV) to, for instance, aP-channel MOSFET that exhibits a gate voltage limit (i.e., agate-to-source voltage limit) of 2.5 volts. The gate driver receives asignal (e.g., a pulse width modulated signal S_(PWM)) from a controller(see, for instance, the controller 120 illustrated and described withrespect to FIG. 1) and a complement of the signal (e.g., a complementarypulse width modulated signal S_(1-PWM)) from the controller.Additionally, the gate driver may provide a first gate drive signal anda second gate drive signal to drive multiple switches such as the mainand auxiliary switches Q_(mn), Q_(aux) of a power converter as describedabove. For purposes of the following discussion, however, the driverwill be described and is adapted to provide a gate drive signal S_(DRV).

The gate driver includes switching circuitry formed by a plurality ofdriver switches such as first, second, third, fourth, fifth, sixth,seventh and eighth driver switches Q_(DR1), Q_(DR2), Q_(DR3), Q_(DR4),Q_(DR5), Q_(DR6), Q_(DR7), Q_(DR8) coupled to a source of electricalpower for the power converter and the controller of the power converter.The gate driver is also coupled to a first bias voltage source thatprovides a first bias voltage V_(bias1), which may be internally orexternally generated and may depend on an input voltage V_(in) of thepower converter. For purposes of the discussion herein, it is assumedthat the first, second, third, fourth, fifth, sixth, seventh and eighthdriver switches Q_(DR1), Q_(DR2), Q_(DR3), Q_(DR4), Q_(DR5), Q_(DR6),Q_(DR7), Q_(DR8) have a low gate voltage limit and a higher voltagedrain. Thus, the first, second, third, fourth, fifth, sixth, seventh andeighth driver switches Q_(DR1), Q_(DR2), Q_(DR3), Q_(DR4), Q_(DR5),Q_(DR6), Q_(DR7), Q_(DR8) may exhibit a low gate voltage limit (e.g. 2.5volts) and at the same time handle drain-to-source voltages above thegate voltage limit thereof (e.g., at least ten volts).

To simplify the discussion, it is also assumed that the first, second,third, fourth, fifth, sixth, seventh and eighth driver switches Q_(DR1),Q_(DR2), Q_(DR3), Q_(DR4), Q_(DR5), Q_(DR6), Q_(DR7), Q_(DR8) exhibit agate threshold voltage of about is 0.5 volts, which is consistent with anumber of fine feature size, low voltage MOSFET designs. The gatethreshold voltage provides a voltage level above or below which(depending on the type) the first, second, third, fourth, fifth, sixth,seventh and eighth driver switches Q_(DR1), Q_(DR2), Q_(DR3), Q_(DR4),Q_(DR5), Q_(DR6), Q_(DR7), Q_(DR8) are enabled to conduct.

In the illustrated embodiment, the first, second, seventh and eighthdriver switches Q_(DR1), Q_(DR2), Q_(DR7), Q_(DR8) are N-channel MOSFETsand the third, fourth, fifth and sixth driver switches Q_(DR3), Q_(DR4),Q_(DR5), Q_(DR6) are P-channel MOSFETs. The drain terminals of thesecond, third and fifth driver switches Q_(DR2), Q_(DR3), Q_(DR5) arecoupled together at a first node n₁. The drain terminals of the first,fourth and sixth driver switches Q_(DR1), Q_(DR4), Q_(DR6) are coupledtogether at a second node n₂. While each of the first, second, seventhand eighth driver switches Q_(DR1), Q_(DR2), Q_(DR7), Q_(DR8) areillustrated with gate, source and drain terminals, it is also common foreach of the first, second, seventh and eighth driver switches Q_(DR1),Q_(DR2), Q_(DR7), Q_(DR8) to include a body terminal.

The gate driver is coupled between an input voltage V_(in) (e.g., anunregulated input voltage at a nominal five volts) of the powerconverter and ground, with a potential difference therebetween for thepurposes of this discussion of five volts. The source terminal of thethird and sixth driver switches Q_(DR3), Q_(DR6) are coupled to theinput voltage V_(in). The first bias voltage V_(bias1), assumed for thisdiscussion to be 2.5 volts with respect to the ground, is coupled to thegate terminal of the fourth and fifth driver switches Q_(DR4), Q_(DR5),and a return connection of the first bias voltage source is coupled tothe ground. The first bias voltage source may or may not be derived fromthe source of electrical power that provides the input voltage V_(in),depending on the application for the gate driver.

As illustrated, the seventh and eighth driver switches Q_(DR7), Q_(DR8)are parallel coupled to the fourth and fifth driver switches Q_(DR4),Q_(DR5), respectively. The seventh and eighth driver switches Q_(DR7),Q_(DR8) include a higher voltage source and a higher voltage drain andtypically exhibit a higher source-to-gate voltage handling capability(e.g., five volts) when the source is more positive than the gate and atthe same time handle drain-to-source voltages above the low gate voltagelimit thereof. The gate terminal of the seventh and eighth driverswitches Q_(DR7), Q_(DR8) are coupled together and to a second voltagebias source that provides a second bias voltage V_(bias2), which may beinternally or externally generated and may depend on an input voltageV_(in) of the power converter.

The gate driver, in the illustrated embodiment, can operate in a coupleof different modes of operation. For instance, when the input voltageV_(in) to the power converter is greater than an upper gate voltagelimit for a main switch Q_(mn) such as a P-channel MOSFET (see, as anexample, the power train of the power converter illustrated anddescribed with respect to FIG. 1) driven by the gate driver, thenvoltage protective features of the gate driver are enabled.

More specifically, when the pulse width modulated signal S_(PWM)provided to the second driver switch Q_(DR2) is high (i.e., when thepulse width modulated signal S_(PWM) is more positive than the gatethreshold voltage of 0.5 volts), the first node n₁ that couples thedrain terminals of the second and third driver switches Q_(DR2), Q_(DR3)is pulled low by the second driver switch Q_(DR2). The drain terminal ofthe fifth driver switch Q_(DR5) is also coupled to the first node n₁ andthe gate terminal thereof is coupled to the first bias voltage source.Thus, the source of the fifth driver switch Q_(DR5) is pulled down tothree volts (i.e., one gate threshold voltage value more positive thanthe first bias voltage V_(bias1)). The gate drive signal S_(DRV) istherefore pulled down two volts below the input voltage V_(in), which isa sufficient voltage to enable a switch such as the main switch Q_(mn),a P-channel MOSFET, illustrated and described with respect to the powertrain of the power converter of FIG. 1 to conduct.

When the complementary pulse width modulated signal S_(1-PWM) providedto the first driver switch Q_(DR1) is more positive than the gatethreshold voltage, the first driver switch Q_(DR1) is enabled to conductand the second node n₂ is pulled down to substantially the groundvoltage by an on-resistance of the first driver switch Q_(DR1). The gateof the third driver switch Q_(DR3) is pulled down to about three volts(i.e., one gate threshold voltage value more positive than the firstbias voltage V_(bias1)). Thus, the third driver switch Q_(DR3) isenabled to conduct and the drain thereof, coupled to first node n₁, ispulled up substantially to the input voltage V_(in). The fifth driverswitch Q_(DR5) is now enabled to conduct because the gate voltage ismore than one gate threshold voltage more negative than the drainthereof, and the source of the fifth driver switch Q_(DR5) is pulled upsubstantially to the input voltage V_(in). Therefore, the gate drivesignal S_(DRV) from the gate driver is also pulled up to substantiallythe input voltage V_(in), which is a sufficient voltage to transition aswitch such as the main switch Q_(mn), a P-channel MOSFET, illustratedand described with respect to the power train of the power converter ofFIG. 1 to a non-conducting state.

Accordingly, a type of level shifting gate driver has been introducedwith an improved level-shifting capability that can controllably raisethe gate voltage of an exemplary switch (e.g., a P-channel MOSFET) tosubstantially the input voltage V_(in) to transition the switch to anon-conducting state, and controllably reduce the gate voltage to alower voltage to enable the switch to conduct. Inasmuch as the gateterminal of the fifth driver switch Q_(DR5) is coupled to the first biasvoltage source, the fifth driver switch Q_(DR5) is transitioned to anon-conducting state when a voltage present on its source is less thanthe first bias voltage V_(bias1) plus its gate threshold voltage(treating the gate threshold voltage of a P-channel MOSFET as a positivenumber). If the gate driver properly applies the first bias voltageV_(bias1) (e.g., if the first bias voltage V_(bias1) is the inputvoltage V_(in) minus 2.5 volts and adjusted for the gate thresholdvoltage of the fifth driver switch Q_(DR5)), the gate drive signalS_(DRV) will not decrease more than 2.5 volts below input voltage V_(in)thereby not exceeding the gate voltage limit of the switch to be driven.The first bias voltage V_(bias1), therefore, is preferably dependent onthe input voltage V_(in). The gate terminal of the switch (again, aP-channel MOSFET) coupled to the gate driver will thus be protected bythe gate driver and, in particular, by the fifth driver switch Q_(DR5),which operatively provides a protective voltage limiting function.Finally, the gate driver is symmetrical and as the pulse width modulatedsignal S_(PWM) and complementary pulse width modulated signal S_(1-PWM)alternate, the conduction states and voltages within the gate driveralternate accordingly.

Additionally, in this mode of operation, the second bias voltageV_(bias2) provided to the gate terminals of the seventh and eighthdriver switches Q_(DR7), Q_(DR8) is at a ground potential. Since thesource terminals of the seventh and eighth driver switches Q_(DR7),Q_(DR8) are not coupled to a potential at or below the ground potential,the seventh and eighth driver switches Q_(DR7), Q_(DR8) are not enabledto conduct as a consequence of the grounded gate terminals thereof.Thus, under the aforementioned circumstances, the seventh and eighthdriver switches Q_(DR7), Q_(DR8) have little effect on the operation ofthe gate driver.

In another operating mode for the gate driver (enabled by the seventhand eighth driver switches Q_(DR7), Q_(DR8)), the input voltage V_(in)to the power converter is not greater than an upper gate voltage limitfor a main switch Q_(mn) such as a P-channel MOSFET (see, as an example,the power train of the power converter illustrated and described withrespect to FIG. 1) driven by the gate driver, then voltage protectivefeatures of the gate driver are not necessary. In this mode ofoperation, the clamping operation of the fifth driver switch Q_(DR5) onthe gate drive signal S_(DRV) is inoperative. More specifically, thegate terminal of the seventh and eighth driver switches Q_(DR7), Q_(DR8)are coupled to a suitably high potential such as the input voltageV_(in). As a result, the seventh and eighth driver switches Q_(DR7),Q_(DR8) are enabled to conduct. Thus, the gate drive signal S_(DRV) iscoupled to ground potential by an on resistance of the second and eighthdriver switches Q_(DR2), Q_(DR8) when the main switch Q_(mn), aP-channel MOSFET as discussed above, driven by the gate driver isenabled to conduct. The gate driver, therefore, selectively providesadditional flexibility by altering a voltage applied to an inputthereof, consequently accommodating an input voltage V_(in) above orbelow a gate voltage limit of a switch driven therefrom. Additionally,for a more detailed analysis of this embodiment of the driver, see U.S.Pat. No. 7,330,017, entitled “Driver for a Power Converter and Method ofDriving a Switch Thereof,” to Dwarakanath, et al., issued Feb. 12, 2008,which is incorporated herein by reference.

Turning now to FIGS. 4 through 17, illustrated are cross-sectional viewsof an embodiment of constructing a semiconductor device embodied in, orportions thereof, an integrated circuit according to the principles ofthe present invention. Beginning with FIG. 4, illustrated is across-sectional view of an embodiment of a partially completedsemiconductor device including isolation regions (e.g., shallow trenchisolation regions) 410 constructed in accordance with one or moreaspects of the present invention. In accordance with standard practicesin the semiconductor industry, various features in this and subsequentdrawings are not drawn to scale. The dimensions of the various featuresmay be arbitrarily increased or decreased for clarity of the discussionherein and like reference numbers may be employed for analogous featuresof different devices that make up the semiconductor device.

The semiconductor device includes a semiconductor substrate (alsoreferred to as a “substrate”) 415 and grown on a surface thereof is anepitaxial layer (e.g., a P-type epitaxial layer) 416, preferably dopedbetween 1·10¹⁴ and 1·10¹⁶ atoms/cm³. The epitaxial layer 416 may not beneeded, particularly if the substrate 415 is a lightly doped P-type.Although in the illustrated embodiment, the substrate 415 is a P-typesubstrate, one skilled in the art understands that the substrate 415could be an N-type substrate, without departing from the scope of thepresent invention.

The substrate 415 is divided into four dielectrically separated areas toaccommodate, in the illustrated embodiment, four transistors (e.g.,MOSFETs) located thereon. More specifically, the substrate 415 canaccommodate a PMOS device and a NMOS device that operate as low voltagedevices within, for instance, a controller of a power converter (i.e.,the control and signal processing devices). Additionally, the substrate415 can accommodate a P-LDMOS device and a N-LDMOS device (alsogenerally referred to as a “LDMOS device and another LDMOS device,” andvice-versa) that operate as higher voltage devices within, for instance,a power train and driver of a power converter (i.e., the power switchesand driver switches).

The shallow trench isolation regions 410 are formed within the epitaxiallayer 416 of the substrate 415 to provide dielectric separation betweenthe devices implemented on the substrate 415. The shallow trenchisolation regions 410 are formed by masking the substrate 415 and usinga photoresist to define the respective regions therein. The shallowtrench isolation regions 410 are then etched and backfilled with adielectric such as silicon dioxide, silicon nitride, a combinationthereof, or any other suitable dielectric material. Then, the epitaxiallayer of the substrate 415 and the shallow trench isolation regions 410are planarized by a lapping process. The steps of masking, etching,backfilling with the dielectric and lapping are well known in the artand will not hereinafter be described in further detail.

Turning now to FIG. 5, illustrated is a cross-sectional view of anembodiment of a partially completed semiconductor device including aburied layer (e.g., an N-type buried layer, also generally referred toas an “oppositely doped buried layer”) 420 constructed in accordancewith one or more aspects of the present invention. As illustrated, theN-type buried layer 420 is recessed within the epitaxial layer 416 ofthe substrate 415 in the area that accommodates the P-LDMOS device andthe N-LDMOS device. The N-type buried layer 420 is formed by a deep ionimplantation process (e.g., at a controlled voltage of about 200kiloelectronvolts) of an appropriate dopant specie such as arsenic orphosphorus and results in a doping concentration profile, preferably ina range of 1·10¹⁸ to 1·10²⁰ atoms/cm³. The N-type buried layer 420 ispreferably located approximately one micrometer below a top surface ofthe epitaxial layer 416 of the substrate 415, and is annealed (e.g., at600 to 1200 degrees Celsius) as necessary to provide the properdistribution of the implanted ion specie. A lateral location of theN-type buried layer 420 is controlled by a photoresist mask usingtechniques well known in the art. The steps of masking, ion implantingand annealing are well known in the art and will not hereinafter bedescribed in further detail.

Turning now to FIG. 6, illustrated is a cross-sectional view of anembodiment of a partially completed semiconductor device including wells(e.g., N-type wells, also generally referred to as an “oppositely dopedwells”) 425 constructed in accordance with one or more aspects of thepresent invention. The N-type wells 425 are constructed with similardoping concentration profiles employing an ion implantation process. TheN-type wells 425 are formed in the epitaxial layer 416 of the substrate415 in the areas that accommodate the PMOS device and the P-LDMOSdevice, and under the shallow trench isolation regions 410 above theN-type buried layer 420 (for the P-LDMOS). The N-type wells 425 areformed to provide electrical isolation for the PMOS device and theP-LDMOS device and operate cooperatively with the N-type buried layer420 (in the case of the P-LDMOS device) and the shallow trench isolationregions 410 to provide the isolation.

A photoresist mask defines the lateral areas for the ion implantationprocess. After the ion implantation process, the implanted specie isdiffused by annealing the substrate 415 at elevated temperature. Anappropriate dopant specie such as arsenic or phosphorus can be used toform the N-type wells 425, preferably, but without limitation, in aretrograde doping concentration profile with approximately 1·10¹⁷atoms/cm³ in the middle, and a higher doping concentration profile atthe surface as well as at the bottom. The steps of masking, ionimplanting and annealing are well known in the art and will nothereinafter be described in further detail.

A width of the N-type wells 425 may vary depending on the particulardevices and application and, as one skilled in the art knows, may belaterally defined by the photoresist mask. For instance, the N-type well425 above the N-type buried layer 420 does not cover the entire areathat accommodates the P-LDMOS device in the epitaxial layer 416 of thesubstrate 415 between the shallow trench isolation regions 410 thereof.The advantages of forming the N-type well 425 in the epitaxial layer 416of the substrate 415 within a portion of the area that accommodates theP-LDMOS device will become more apparent for the reasons as set forthbelow.

Turning now to FIG. 7, illustrated is a cross-sectional view of anembodiment of a partially completed semiconductor device including wells(e.g., P-type wells, also generally referred to as an “oppositely dopedwells”) 430 constructed in accordance with one or more aspects of thepresent invention. The P-type wells 430 are formed with similar dopingconcentration profiles by ion implantation process of an appropriatespecie such as boron. The P-type wells 430 are formed in the epitaxiallayer 416 of the substrate 415 between the shallow trench isolationregions 410 substantially in the areas that accommodate the NMOS deviceand N-LDMOS device. A photoresist mask defines the lateral areas for theion implantation process. After the ion implantation process, theimplanted specie is diffused by annealing the substrate 415 at anelevated temperature.

Again, an appropriate dopant specie such as boron can be used to formthe P-type wells 430, preferably resulting in a retrograde dopingconcentration profile with approximately 1·10¹⁷ atoms/cm³ in the middle,and a higher doping concentration profile at the top surface as well asat the bottom. The steps of masking, ion implanting and annealing arewell known in the art and will not hereinafter be described in furtherdetail. Analogous to the N-type wells 425, a width of the P-type wells430 may vary depending on the particular devices and application and, asone skilled in the art knows, may be laterally defined by thephotoresist mask. For instance, while the P-type well 430 above theN-type buried layer 425 covers the entire area that accommodates theN-LDMOS device in the epitaxial layer 416 of the substrate 415 betweenthe shallow trench isolation regions 410 thereof, it is well within thebroad scope of the present invention to define the P-type well 430 tocover a portion of the area that accommodates the N-LDMOS device in theepitaxial layer 416 of the substrate 415.

Turning now to FIG. 8, illustrated is a cross-sectional view of anembodiment of a partially completed semiconductor device includingN-type implant 427 and P-type implant 432 to form channel extensions(“CE”) for the P-LDMOS and N-LDMOS devices, constructed in accordancewith one or more aspects of the present invention. For a laterallyconstructed device such as a power device, drain current generally flowsalong the surface of a drift region of the device, thereby creating anelectric field in the same direction as the drift current. The channelextension performs a blocking function that operates on the electricfield in this region to reduce the curvature of the associated electricpotential, thereby delaying the onset of breakdown. At breakdown, theelectric field that is associated with the channel extension is moreuniform than the electric field that would be produced without thechannel extension. The channel extension can be inserted into theprocess flow in a well-controlled manner so that a reasonable tradeoffcan be achieved between a breakdown voltage, on-resistance, and hotcarrier injection (“HCI”). Hot carrier injection is an undesirableeffect in high-voltage lateral devices that can significantly degradedevice performance and long-term quality, particularly for higher drainvoltages. By careful selection of the various parameters that define thechannel extension, the hot carrier injection effects can be managed.

The N-type implant 427 that forms the channel extension is formed of thesame doping type or like type as the N-type well 425 in which it isdeposited, and may be doped with the same or with a different atomicspecie and with a doping concentration profile, preferably about1.2·10¹⁸ atoms/cm³. Similarly, the P-type implant 432 is formed as achannel extension of the same doping type or like type as the P-typewell 430 in which it is deposited, but it too may be formed with thesame or with a different atomic specie and with a doping concentrationprofile, preferably about 1.2·10¹⁸ atoms/cm³. Additional exemplarydimensions and depth of the implants 427, 432 will be described furtherbelow. The implants 427, 432 are preferably formed with an ionimplantation process including masking and patterning steps employingtechniques well understood in the art to define lateral physicaldimensions thereof.

Turning now to FIG. 9, illustrated is a cross-sectional view of anembodiment of a partially completed semiconductor device including gates440 for the PMOS, NMOS, P-LDMOS and N-LDMOS devices constructed inaccordance with one or more aspects of the present invention. Theprocess of forming the gates 440 is preceded by forming gate dielectriclayer 435 over the semiconductor device of a thickness consistent withthe intended operating voltage of the gates 440. The dielectric materialis typically silicon dioxide with a thickness of about five nanometersfor devices employing about 0.25-micrometer feature sizes and operatingat low gate voltages (e.g., 2.5 volts). Assuming the gate-to-sourcevoltage limit of the P-LDMOS and N-LDMOS devices is limited to a lowervoltage (e.g., 2.5 volts) and the PMOS and NMOS devices operate at thesame voltage, then the gate dielectric layer 435 can be formed withdimensions as set forth above. Preferably, the gate dielectric layer 435is constructed with a uniform thickness to provide a gate-to-sourcevoltage rating for the devices of approximately 2.5 volts thatcompletely or nearly completely saturates the forward conductionproperties of the device. Of course, the aforementioned voltage rangefor the devices is provided for illustrative purposes only and othervoltage ranges are within the broad scope of the present invention.

Next, a polysilicon layer is deposited over a surface of the gatedielectric layer 435 and doped N-type or P-type, using an appropriatedoping specie. The polysilicon layer is annealed at an elevatedtemperature to properly diffuse the dopant. A photoresist mask isemployed with an etch to define the lateral dimensions to define thegates 440. The steps of depositing the dielectric and polysiliconlayers, doping, annealing, and patterning are well known in the art andwill not hereinafter be described in further detail. Alternatively, thegates 440 may include a wide range of materials including variousmetals, doped semiconductors, or other conductive materials.Additionally, the gates 440 may have a wide range of thicknesses. Thethickness of the gates 440 may range from about 100 to about 500nanometers, but may be even smaller or larger depending on theapplication.

The underlying gate dielectric layer 435 and the gates 440 are formedusing conventional processes and will not hereinafter be described infurther detail. The conventional processes include, but are not limitedto, thermal oxidation, chemical vapor deposition, physical vapordeposition, epitaxial growth, or other similar process. It is recognizedthat the gate dielectric layer 435 and gates 440 may have differentthicknesses in different areas of the substrate 415 without departingfrom the scope of the present invention.

Turning now to FIG. 10, illustrated is a cross-sectional view of anembodiment of a partially completed semiconductor device including alightly doped region (e.g., a N-type lightly doped region) 445 of adrain (also referred to as a “N-type lightly doped drain region”) forthe N-LDMOS device constructed in accordance with one or more aspects ofthe present invention. The N-type lightly doped drain region 445 allowsthe N-LDMOS device to accommodate higher voltage operation from thedrain to the source thereof. The N-type lightly doped drain region 445may be formed employing an ion implantation process in connection with aphotoresist mask to define the lateral dimensions thereof. Additionally,an annealing process at elevated temperatures distributes the implantedion specie. The N-type lightly doped drain region 445 is preferablydoped, without limitation, to about 1·10¹⁶ to 1·10¹⁷ atoms/cm³. Thesteps of patterning, ion implanting and annealing are well known in theart and will not hereinafter be described in further detail.

Turning now to FIG. 11, illustrated is a cross-sectional view of anembodiment of a partially completed semiconductor device including alightly doped region (e.g., a P-type lightly doped region) 450 of adrain (also referred to as a “P-type lightly doped drain region”) forthe P-LDMOS device constructed in accordance with one or more aspects ofthe present invention. The P-type lightly doped drain region 450 allowsthe P-LDMOS device to accommodate higher voltage operation from thedrain to the source thereof. The P-type lightly doped drain region 450may be formed employing an ion implantation process in connection with aphotoresist mask to define the lateral dimensions thereof. Additionally,an annealing process at elevated temperatures distributes the implantedion specie. The P-type lightly doped drain region 450 is preferablydoped, without limitation, to about 1·10¹⁶ to 1·10¹⁷ atoms/cm³. Thesteps of patterning, ion implanting and annealing are well known in theart and will not hereinafter be described in further detail.

The N-type and P-type lightly doped drain regions 445, 450 providehigher voltage drains for the N-LDMOS and P-LDMOS devices, respectively.In effect, the N-type and P-type lightly doped drain regions 445, 450form parasitic diodes with adjoining oppositely doped wells, namely, theP-type well 430 and N-type well 425, respectively. The breakdown voltageof the parasitic diodes is determined by the doping concentrationprofiles, with lighter doping concentration profiles providing a higherbreakdown voltage because the resulting internal electric fields aredistributed over longer distances when the diodes are back biased. It isrecognized that the width of the N-type and P-type lightly doped drainregions 445, 450 may be individually varied to alter the breakdownvoltage characteristics of the respective N-LDMOS and P-LDMOS deviceswithout departing from the scope of the present invention.

Turning now to FIG. 12, illustrated is a cross-sectional view of anembodiment of a partially completed semiconductor device including gatesidewall spacers 455 about the gates 440 constructed in accordance withone or more aspects of the present invention. The gate sidewall spacers455, which may be formed from an oxide or other dielectric material, aregenerally formed by depositing a nitride followed by an etching process.The material forming the gate sidewall spacers 455 may be the same ordifferent from the dielectric material used for the gate dielectriclayer 435.

Turning now to FIG. 13, illustrated is a cross-sectional view of anembodiment of a partially completed semiconductor device includingheavily doped regions for the source and drain (often referred toindividually as a “source/drain” and together as a “source/drain andanother source/drain,” and vice-versa) of the NMOS and N-LDMOS devicesconstructed in accordance with one or more aspects of the presentinvention. The heavily doped regions (e.g., N-type heavily dopedregions) 460 for the source and drain of the NMOS device preferably havea different doping concentration profile than the heavily doped regions(e.g., N-type heavily doped regions) 462 for the source and drain of theN-LDMOS device. The N-type heavily doped regions 460 for the NMOS deviceare formed within the P-type well 430 thereof and, as alluded to above,form the source and the drain for the NMOS device. Additionally, theN-type heavily doped regions 462 for the N-LDMOS device are formedwithin the P-type well 430 thereof and, as alluded to above, form thesource and a portion of the drain for the N-LDMOS device. Also, theN-type heavily doped region 462 of the drain for the N-LDMOS device isadjacent the N-type lightly doped drain region 445 thereof.

The N-type heavily doped regions 460, 462 may be advantageously formedwith an ion implantation process using a dopant specie such as arsenicor phosphorus. The doping process includes a photoresist mask to definelateral dimensions of the N-type heavily doped regions 460, 462 and anannealing process at elevated temperature to properly distribute theimplanted specie. The N-type heavily doped region 460 for the source anddrain of the NMOS device is doped, without limitation, to be greaterthan about 1·10¹⁹ atoms/cm³. The N-type heavily doped region 462 for thesource and drain of the N-LDMOS device is doped, without limitation, tobe greater than about 5·10¹⁹ atoms/cm³. Incorporating the differentdoping concentration profiles of the N-type heavily doped regions 460,462 for the source and drain of the NMOS and N-LDMOS devices typicallyadds additional processing steps to the design thereof. It should beunderstood, however, that the N-type heavily doped regions 460, 462 forthe source and drain of the NMOS and N-LDMOS devices may incorporate thesame or analogous doping concentration profiles and still be within thebroad scope of the present invention. Inasmuch as the steps ofpatterning, ion implanting and annealing are well known in the art, theprocesses will not hereafter be described in further detail.

Turning now to FIG. 14, illustrated is a cross-sectional view of anembodiment of a partially completed semiconductor device includingheavily doped regions for the source and drain for the PMOS and P-LDMOSdevices constructed in accordance with one or more aspects of thepresent invention. The heavily doped regions (e.g., P-type heavily dopedregions) 465 for the source and drain of the PMOS device preferably havea different doping concentration profile than the heavily doped regions(e.g., P-type heavily doped regions) 467 for the source and drain of theP-LDMOS device. The P-type heavily doped regions 465 for the PMOS deviceare formed within the N-type well 425 thereof and, as alluded to above,form the source and the drain for the PMOS device. Additionally, theP-type heavily doped regions 467 for the P-LDMOS device are formedwithin the N-type well 425 or in a region adjacent the N-type well 425thereof and, as alluded to above, form the source and a portion of thedrain for the P-LDMOS device. Also, the P-type heavily doped region 467of the drain for the P-LDMOS device is adjacent the P-type lightly dopeddrain region 450 thereof.

The P-type heavily doped regions 465, 467 may be advantageously formedwith an ion implantation process using dopant specie such as boron. Thedoping process includes a photoresist mask to define lateral dimensionsof the P-type heavily doped regions 465, 467 and an annealing process atelevated temperature to properly distribute the implanted specie. TheP-type heavily doped region 465 for the source and drain of the PMOSdevice is doped, without limitation, to be greater than about 1·10¹⁹atoms/cm³. The P-type heavily doped region 467 for the source and drainof the P-LDMOS device is doped, without limitation, to be greater thanabout 5·10¹⁹ atoms/cm³. Incorporating the different doping concentrationprofiles of the P-type heavily doped regions 465, 467 for the source anddrain of the PMOS and P-LDMOS devices typically adds additionalprocessing steps to the design thereof. It should be understood,however, that the P-type heavily doped regions 465, 467 for the sourceand drain of the PMOS and P-LDMOS devices may incorporate the same oranalogous doping concentration profiles and still be within the broadscope of the present invention. Inasmuch as the steps of patterning, ionimplanting and annealing are well known in the art, the processes willnot hereafter be described in further detail.

The annealing process described above with respect to FIG. 14 inherentlyanneals the previously doped regions of the semiconductor device aswell. As is well understood in the art, the cumulative time-temperaturefunction for the annealing processing steps is a factor in integratedcircuit design to provide proper “drive-in” of the implanted specie. Thetime period, temperature range and selected steps to perform theannealing processes may vary depending on an application and the desiredresults to form a semiconductor device incorporated into an integratedcircuit. Thus, it is contemplated that the annealing processes may beperformed after each ion implantation process as described herein ordelayed until after several ion implantation processes and still achievethe desired results.

As mentioned above, the N-type well 425 above the N-type buried layer420 does not cover the entire area that accommodates the P-LDMOS devicein the epitaxial layer 416 of the substrate 415 between the shallowtrench isolation regions 410 thereof. In particular, the N-type well 425covers about half of the area that accommodates the P-LDMOS devicethrough a channel region (some of which is designated 470) that isadjacent to and extends between the P-type heavily doped region 467 ofsource and the P-type lightly doped drain region 450 of the drain, andunder the gate 440 thereof recessed into the substrate 415 (or theoverlying epitaxial layer 416). In other words, the N-type well 425extends under and within the channel region 470, and the N-type well 425and N-type buried layer 420 are oppositely doped in comparison to theP-type lightly doped drain region 450 and P-type heavily doped region467. For purposes of clarity, the channel region 470 is generallydefined and well understood to be a conductive region between the sourceand drain (or the lightly or heavily doped regions thereof) of atransistor that is induced under the gate by a charge thereon. Thus, adoped region (e.g., a P-type doped region) 472 extends between theP-type heavily doped region 467 and the N-type well 425 of the P-LDMOSdevice (under a portion of the P-type lightly doped drain region 450)and has a doping concentration profile less than a doping concentrationprofile of the P-type heavily doped region 467.

In the illustrated embodiment, the P-type doped region 472 happens to beembodied in the epitaxial layer 416, which has a doping concentrationprofile between 1·10¹⁴ and 1·10¹⁶ atoms/cm³. Employing the epitaxiallayer 416 as the P-type doped region 472 provides an opportunity to omita masking and a processing step in the manufacture of the semiconductordevice. Of course, the epitaxial layer 416 may be omitted and the P-typedoped region 472 may be formed in the substrate 415 (in this case, aP-type doped substrate). In yet another alternative embodiment, theP-type doped region 472 may be formed by an ion implantation processprior to implanting the P-type heavily doped region 467 for the drain ofthe P-LDMOS device. In such a case, the P-type doping material such asboron would be implanted to provide a doping concentration profile lessthan a doping concentration profile of the P-type heavily doped region467. Of course, the P-type doped region 472 may be formed with anydoping concentration profile less than the P-type heavily doped region467 including a doping concentration profile less than the P-typelightly doped drain region 450 and still be within the broad scope ofthe present invention.

Incorporating the P-type doped region 472 into the P-LDMOS deviceincreases a breakdown voltage between the P-type heavily doped region467 and the N-type well 425 of the P-LDMOS device. More specifically, ineffect the P-type doped region 472 forms a parasitic diode with theadjoining oppositely doped N-type well 425. The breakdown voltage of theparasitic diode is determined by the doping concentration profiles, withlighter doping concentration profiles providing a higher breakdownvoltage because the resulting internal electric fields are distributedover longer distances when the diodes are back biased. Thus, the P-LDMOSdevice exhibits a higher drain-to-source voltage handling capability dueto the higher breakdown voltage thereof. Thus, the P-LDMOS device canhandle voltages, without limitation, of at least ten volts whileconstructed on the same substrate 415 as the CMOS devices, namely, thePMOS and NMOS devices that operate at lower voltages (e.g., 2.5 volts).It should be understood that while the doped region has been describedwith respect to the P-LDMOS device, the principles are equallyapplicable to the N-LDMOS device and, for that matter, other transistorsof analogous construction.

Turning now to FIG. 15, illustrated is a cross-sectional view of anembodiment of a partially completed semiconductor device including asalicide layer (one of which is designated 475) on the gate, source anddrain of the NMOS, PMOS, N-LDMOS and P-LDMOS devices constructed inaccordance with one or more aspects of the present invention. As clearlyunderstood by those skilled in the art, the formation of the salicidelayer 475 refers to deposition of a metal over silicon by a sputteringor other deposition process followed by an annealing process to improvea conductivity of polysilicon or other material and to facilitate theformation of ohmic contacts.

First, a region for salicidation is exposed using a photoresist mask toselectively etch the gate dielectric layer 435 from the source and drainof the NMOS, PMOS, N-LDMOS and P-LDMOS devices. Then, a metal, generallytitanium, is deposited and the substrate 415 is annealed at an elevatedtemperature. During the annealing process, metal in contact with siliconreacts with silicon to form the salicide layer 475. The metal not incontact with silicon remains as metal, which can be etched away, leavingbehind the salicide layer 475. The steps of masking, depositing metal,annealing and etching are well known in the art and will not hereinafterbe described in further detail.

Turning now to FIG. 16, illustrated is a cross-sectional view of anembodiment of a partially completed semiconductor device includingdielectric regions 480 for defining metal contacts constructed inaccordance with one or more aspects of the present invention. Thesemiconductor device is illustrated following a masking, deposition andetching of a dielectric layer to define the dielectric regions 480. Thedielectric regions 480 may be formed from an oxide or other suitabledielectric material. The dielectric regions 480 are generally formed byblanket depositing the dielectric layer over the surface of thepartially completed semiconductor device and anisotropically etching thedielectric layer, resulting in the dielectric regions 480. The steps ofdepositing the dielectric layer, masking and etching are well known inthe art and will not hereinafter be described in further detail.

Turning now to FIG. 17, illustrated is a cross-sectional view of thesemiconductor device including metal (ohmic) contacts 485 formed overthe salicide layer 475 on the gate, source and drain of the NMOS, PMOS,N-LDMOS and P-LDMOS devices constructed in accordance with one or moreaspects of the present invention. The embodiment illustrates thesemiconductor device following deposition and patterning of a metal(e.g., aluminum) for the metal contacts 485. The masking, etching, andfurther deposition of the dielectric and metal layers may be repeatedseveral times to provide multiple, highly conductive layers andinterconnections in accordance with the parameters of the application.For example, a four-level metal interconnection arrangement may beprovided by incorporating several steps to form the multi-level metalcontacts 485. As illustrated, the metal contacts 485 are formed aboutand defined by the dielectric layers 480.

As illustrated in FIG. 17, the N-type implant 427 and the P-type implant432 that form the channel extensions are positioned under the channelregions 470 of the P-LDMOS and the N-LDMOS, respectively. The N-typeimplant 427 extends under a portion of the P-type lightly doped drainregion 450 and the P-type heavily doped region 467 for the P-LDMOS bychannel extension lengths (generally designated 490). The P-type implant432 extends under a portion of the N-type lightly doped drain region 445and the N-type heavily doped region 462 for the N-LDMOS by channelextension lengths (generally designated 490). In general, the implantsextend a short but limited distance beyond the respective gate/channelregion, terminating under the respective lightly and heavily dopedregions. The channel extension lengths 490 are advantageously selectedas described further hereinbelow to provide increased breakdown voltagefor the device and to reduce on-state resistance. The channel extensionlengths 490 may be the same or unequal with respect to the P-LDMOS andN-LDMOS, and also with respect to the lightly and heavily doped regionsof a LDMOS. Exemplary parameters for the design of a channel extensionand the respective lightly doped drain region for various semiconductorgeometries include channel extension lengths of 0.3 μm (both lengthsequal), channel extension dose of 1·10¹³ cm⁻², channel extension energyof 160 kilovolts (“kV”), length (designated 451) of lightly doped drainregion of 0.6 μm, and lightly doped drain dose of 5·10¹² cm⁻².

TABLE I below illustrates the effect on device breakdown voltage,on-state resistance, saturation current, and threshold voltage due tovarying the lightly doped drain region (or “lightly doped drain”) dosefor a fixed channel extension length, channel extension dose, andchannel extension energy. Substantial effects on breakdown voltage,on-state resistance, and saturation current can be observed in the data.As can be seen in TABLE I below, the effect of varying the lightly dopeddrain dose on threshold voltage is not substantial.

TABLE I Impact of Varying the Lightly Doped Drain Dose lightly channelchannel channel doped lightly break- on-state saturation extensionextension extension drain doped down resistance current threshold lengthdose energy length drain dose voltage [ohm (“Ω”) · [microamperes voltage[μm] [cm⁻²] [kV] [μm] [cm⁻²] [V] cm²] (“μA”) · cm⁻²] [V] 0.25 1 · 10¹³200 0.6 7 · 10¹² 13.7 416 236 0.6 0.25 1 · 10¹³ 200 0.6 5 · 10¹² >19 555196 0.6 0.25 1 · 10¹³ 200 0.6 3.5 · 10¹²   >19 806 161 0.6

TABLE II below illustrates the effect on device breakdown voltage,on-state resistance, saturation current, and threshold voltage due tovarying the channel extension energy (i.e., its depth) for a fixedchannel extension length, channel extension dose, length of the lightlydoped drain, and lightly doped drain dose. Substantial effects onsaturation current can be observed in the data. As can be seen in TABLEII below, the effect of varying the lightly doped drain dose onbreakdown voltage, on-state resistance, and threshold voltage are lesssignificant.

TABLE II Impact of Varying the Channel Extension Energy lightly channelchannel channel doped lightly break- extension extension extension draindoped down on-state saturation threshold length dose energy length draindose voltage resistance current voltage [μm] [cm⁻²] [kV] [μm] [cm⁻²] [V][Ω · cm²] [μA · cm⁻²] [V] 0.25 1 · 10¹³ 200 0.6 5 · 10¹² >19 555 196 0.60.25 1 · 10¹³ 160 0.6 5 · 10¹² >19 555 189 0.6 0.25 1 · 10¹³ 120 0.6 5 ·10¹² 18.1 564 177 0.61

TABLE III below illustrates the effect on device breakdown voltage,on-state resistance, saturation current, and threshold voltage due tovarying the channel extension length for a fixed channel extension dose,channel extension energy, length of the lightly doped drain, and lightlydoped drain dose. Modest or insubstantial effects on breakdown voltage,on-state resistance, saturation current, and threshold voltage can beobserved in the data.

TABLE III Impact of Varying the Channel Extension Length lightly lightlychannel channel channel doped doped break- extension extension extensiondrain drain down on-state saturation threshold length dose energy lengthdose voltage resistance current voltage [μm] [cm⁻²] [kV] [μm] [cm⁻²] [V][Ω · cm²] [μA · cm⁻²] [V] 0.15 1 · 10¹³ 160 0.6 5 · 10¹² >19 555 191 0.60.25 1 · 10¹³ 160 0.6 5 · 10¹² >19 555 196 0.6 0.35 1 · 10¹³ 160 0.6 5 ·10¹² 17.7 570 187 0.6

Turning now to FIG. 18, illustrated is a cross-sectional view of anotherembodiment of a semiconductor device embodied in, or portions thereof,an integrated circuit constructed according to the principles of thepresent invention. Inasmuch as the processing steps to construct thesemiconductor device of FIG. 18 are analogous to the processing stepsdescribed above, the steps in the process will not hereinafter bedescribed in detail. The semiconductor device includes isolation regions(e.g., shallow trench isolation regions) 510 within a substrate 515(e.g., P-type substrate) to provide dielectric separation between PMOS,NMOS, P-LDMOS and N-LDMOS devices. A buried layer (e.g., an N-typeburied layer, also generally referred to as an “oppositely doped buriedlayer”) 520 is recessed within the substrate 515 in the area thataccommodates the P-LDMOS device and the N-LDMOS device.

The semiconductor device also includes wells (e.g., N-type wells,generally referred to as an “oppositely doped buried layer”) 525 formedin the substrate 515 in the areas that accommodate the PMOS device andthe P-LDMOS device, and under the shallow trench isolation regions 510above the N-type buried layer 520 (for the P-LDMOS). The N-type wells525 are formed to provide electrical isolation for the PMOS device andthe P-LDMOS device and operate cooperatively with the N-type buriedlayer 520 (in the case of the P-LDMOS device) and the shallow trenchisolation regions 510 to provide the isolation.

The semiconductor device includes additional wells (e.g., P-type wells,generally referred to as an “oppositely doped buried layer”) 530 formedin the substrate 515 between the shallow trench isolation regions 510substantially in the areas that accommodate the NMOS device and N-LDMOSdevice. While the P-type well 530 above the N-type buried layer 520covers the entire area that accommodates the N-LDMOS device in thesubstrate 515 between the shallow trench isolation regions 510 thereof,it is well within the broad scope of the present invention to define theP-type well 530 to cover only a portion of the area that accommodatesthe N-LDMOS device in the substrate 515. The semiconductor device alsoincludes gates 540 for the PMOS, NMOS, P-LDMOS and N-LDMOS deviceslocated over a gate dielectric layer 535 and including gate sidewallspacers 555 about the gates 540 thereof.

The N-LDMOS device includes lightly doped regions (e.g., N-type lightlydoped regions) 545 for the source and the drain thereof. The P-LDMOSdevice also includes lightly doped regions (e.g., P-type lightly dopedregions) 550 for the source and the drain thereof. In the presentembodiment and for analogous reasons as stated above, the N-type andP-type lightly doped regions 545, 550 provide higher voltage sources anddrains for the N-LDMOS and P-LDMOS devices, respectively. As a result,not only can the N-LDMOS and P-LDMOS devices handle higher voltages fromthe drain-to-source thereof, but the devices can handle a higher voltagefrom a source-to-gate thereof when the source is more positive than thegate 540. It is recognized that the width of the N-type and P-typelightly doped regions 545, 550 may be individually varied to alter thebreakdown voltage characteristics of the respective N-LDMOS and P-LDMOSdevices without departing from the scope of the present invention.Additionally, the N-type and P-type lightly doped regions 545, 550 maybe formed in a manner similar to the respective N-LDMOS and P-LDMOSdevices illustrated and described with respect to FIGS. 4 through 17.

The semiconductor device also includes heavily doped regions (e.g.,N-type heavily doped regions) 560 for the source and drain of the NMOSdevice that preferably have a different doping concentration profilethan heavily doped regions (e.g., N-type heavily doped regions) 562 forthe source and drain of the N-LDMOS device. The N-type heavily dopedregions 560 for the NMOS device are formed within the P-type well 530thereof and, as alluded to above, form the source and the drain for theNMOS device. Additionally, the N-type heavily doped regions 562 for theN-LDMOS device are formed within the P-type well 530 thereof and, asalluded to above, form a portion of the source and the drain for theN-LDMOS device. Also, the N-type heavily doped regions 562 of the sourceand drain for the N-LDMOS device are adjacent the N-type lightly dopeddrain regions 545 thereof.

The semiconductor device also includes heavily doped regions (e.g.,P-type heavily doped regions) 565 for the source and drain of the PMOSdevice that preferably have a different doping concentration profilethan heavily doped regions (e.g., P-type heavily doped regions) 567 forthe source and drain of the P-LDMOS device. The P-type heavily dopedregions 565 for the PMOS device are formed within the N-type well 525thereof and, as alluded to above, form the source and the drain for thePMOS device. Additionally, the P-type heavily doped regions 567 for theP-LDMOS device are formed within the N-type well 525 or in regionsadjacent the N-type well 525 thereof and, as alluded to above, form aportion of the source and the drain for the P-LDMOS device. Also, theP-type heavily doped regions 567 of the source and drain for the P-LDMOSdevice are adjacent the P-type lightly doped drain regions 550 thereof.

While the P-type heavily doped regions 567 preferably have the samedoping concentration profiles, it is well within the broad scope of thepresent invention that the P-type heavily doped region 567 for thesource has a different doping concentration profile than the counterpartof the drain. The same principle applies to other like regions of thedevices of the semiconductor device.

Additionally, whereas the P-LDMOS and N-LDMOS devices illustrated anddescribed with respect to FIGS. 4 through 17 are referred to asasymmetrical devices, the P-LDMOS and N-LDMOS devices illustrated anddescribed with respect to FIG. 18 are referred to as symmetricaldevices. In other words, the symmetrical nature of the source and drainof the semiconductor device of FIG. 18 provide for a symmetrical device.Of course, those skilled in the art should understand that thedimensions of the source and drain (including the lightly and heavilydoped regions thereof) may vary and still fall within the broad scope ofthe present invention, including deviations from symmetry. Thesemiconductor device also includes channel regions (some of which isdesignated 570), metal contacts 585 defined by dielectric regions 580formed over salicide layers (one of which is designated 575) for thegate, source and drain of the PMOS, NMOS, P-LDMOS and N-LDMOS devices.

The semiconductor device also includes an N-type implant 527 and aP-type implant 532 to form channel extensions, and are positioned,respectively, under the channel regions 570 of the P-LDMOS and theN-LDMOS devices. The N-type and P-type implants 527, 532 are formed withchannel extension lengths 590 similar to those described with referenceto the semiconductor device illustrated in FIGS. 4 through 17. Theimplants extend a short but limited distance beyond the respectivegate/channel region, terminating under the respective lightly andheavily doped regions. The channel extension lengths 590 areadvantageously selected as described previously hereinabove to provideincreased breakdown voltage for the device and to reduce on-stateresistance. The channel extension lengths 590 may be the same orunequal. Again, the channel extensions may be of like type to and have adoping concentration profile greater than a doping concentration profileof the respective oppositely doped wells.

The development of a semiconductor device as described herein retainsfine line structures and accommodates an operation at higher voltagesand with higher switching frequencies (e.g., five to ten megahertz). Byintroducing the lightly doped region(s) between the heavily doped regionand oppositely doped well, the LDMOS device exhibits a high voltagehandling capability from the drain to the source thereof. Theintroduction of the channel extension in the oppositely doped well witha same doping polarity as the oppositely doped well and with a lengthextending a distance beyond the gate/channel region and terminatingunder a lightly doped region or heavily doped region advantageouslyenables construction of a device with yet a higher voltage rating thatrequires a smaller active area to achieve a given on-state resistance.At the same time, the higher voltage device is constructed employing alimited number of additional processing steps. Moreover, the LDMOSdevice may exhibit a low-level gate-to-source voltage limit (e.g., 2.5volts) and at the same time handle drain-to-source voltages above thegate-to-source voltage limit thereof. Alternatively, the LDMOS devicemay exhibit a higher level source-to-gate voltage handling capability(e.g., five volts) when the source is more positive than the gate and atthe same time handle drain-to-source voltages above the low levelgate-to-source voltage limit thereof. In other words, the LDMOS devicecan switch the larger currents normally associated with a power train ofa power converter by appropriately designing selected regions thereof asset forth above.

As introduced herein, the channel extension serves as a type of fieldplate beneath the drift region (generally includes, without limitation,the channel region or the region between the source and drain under thegate) within the semiconductor device. The function of the channelextension is to reduce the lateral gradient in the electric field formedwithin the drift region when the drain is biased to a high voltagelevel, resulting in a more constant drift field and, hence, a smallerpeak field. The smaller the peak field in the drift region, the higherthe breakdown voltage of the semiconductor device. A more constant driftregion field is achieved by introducing a vertical component(perpendicular to the silicon-surface) to the electric field in thedrift region to offset the curvature in the lateral direction-parallelto the surface. A vertical electric field component in the drift regionis created by suppressing the depletion of well doping beneath the lightdoped region, pinning the depletion at the location of the channelextension as the drain bias is increased.

Most techniques to balance the drift field with a vertical field causedepletion of the charge in the drift region even at low drain bias, andthis reduces the drive current of the device in its on-state andincreases the on-state series resistance. As introduced herein, thechannel extension is placed at a distance slightly below the lightly orheavily doped region of the drain to ensure that there is littledepletion therein at low drain bias, but increased depletion at higherdrain bias, when it is needed. Furthermore, it is preferable that thechannel extension does not extend fully beneath the lightly doped regionof the drain. This admits a relatively lower overall well doping beneaththe drain, which will increase the depletion region directly beneath thedrain, reduce the drain-to-well electric field at high drain bias, andincrease the drain-to-well breakdown voltage. It will also reduce thedrain capacitance compared to the case in which the channel extension isplaced fully beneath the drain. Masking the channel extension from theregion beneath the drain does not reduce its ability to increase thebreakdown voltage. To balance the drift region field in a preferablemanner, the vertical component of the depletion field beneath thelightly doped region should be larger close to the channel region, andsmaller near the drain.

Finally, the channel extension typically extends beneath the channelregion towards the source. This allows the channel extension to functionas a field plate to increase breakdown voltage, as well as a thresholdvoltage control implant and a punch-through suppression implant toenable high voltage operation at short channel region lengths. A shortchannel region length is better suited to high switching speeds ofinnovative power supplies. It should be noted that, besides a shortchannel region length, the gate oxide should also be thin, andconsistent, with the short channel region length. This combinationenables better transistor performance in terms of switching speed andresponse time. Implemented in this way, the channel extension is anegligible mask adder to an integrated CMOS process that enablesintegrated high-voltage transistors. Such a CMOS process, which combinesshort channel region lengths and thin gate oxides for devices such aspower devices, allows such devices to support high switching speeds withlow on-state resistance and high breakdown voltages.

Thus, a transistor (e.g., a LDMOS device) and related method ofconstructing the same with readily attainable and quantifiableadvantages has been introduced. Those skilled in the art shouldunderstand that the previously described embodiments of the LDMOSdevice, semiconductor device and related methods of constructing thesame are submitted for illustrative purposes only. In addition, otherembodiments capable of producing a higher voltage device such as a LDMOSdevice that can accommodate higher voltages and is capable of beingintegrated with low voltage devices on a semiconductor substrate in anintegrated circuit that may form a power converter or portions thereofare well within the broad scope of the present invention.

In an advantageous embodiment, the LDMOS device and semiconductor devicemay be incorporated into an integrated circuit that forms a powerconverter or the like. Alternatively, the semiconductor device may beincorporated into an integrated circuit that forms another system suchas a power amplifier, motor controller, and a system to control anactuator in accordance with a stepper motor or other electromechanicaldevice.

Turning now to FIG. 19, illustrated is a cross-sectional view of anembodiment of a micromagnetic device employable in an integrated circuitconstructed according to the principles of the present invention. Themicromagnetic device is formed on a substrate 605 (e.g., silicon) andincludes a first insulating layer 610 (e.g., silicon dioxide) formedthereover. Following an electroplating process to form a trench in acenter region of the substrate 605, an adhesive layer (e.g., titanium orchromium) and a first seed layer 615 (e.g., gold or copper) are formedover the first insulating layer 610. Additionally, a first conductivewinding layer 620 of, without limitation, copper, is formed in thetrench that forms a first section of a winding for the micromagneticdevice.

An adhesive layer (e.g., titanium or chromium) and a second insulatinglayer 625 (e.g., silicon dioxide) is formed above the first conductivewinding layer 620. The micromagnetic device also includes first andsecond magnetic core layers 630, 640 with a third insulating layer 635therebetween in a center region of the substrate 605 above the firstconductive winding layer 620. The first and second magnetic core layers630, 640 are typically surrounded by an adhesive layer, seed layer andprotection layer as set forth below with respect to FIG. 20. Also, anadhesive layer may be formed prior to forming the third insulating layer635.

An adhesive layer (e.g., titanium or chromium) and a fourth insulatinglayer 645 (e.g., silicon dioxide) are formed above the second magneticcore layer 640 in the center region of the substrate 605 and over thesecond insulating layer 625 laterally beyond the center region of thesubstrate 605. An adhesive layer (e.g., titanium or chromium) and asecond seed layer 650 (e.g., gold or copper) are formed above the fourthinsulating layer 645 in the center region of the substrate 605 and invias down to the first conductive winding layer 620 about the centerregion of the substrate 605. A second conductive winding layer 655 isformed above the second seed layer 650 and in the vias to the firstconductive winding layer 620. The second conductive winding layer 655 isformed of, without limitation, copper and forms a second section of awinding for the micromagnetic device. Thus, the first conductive windinglayer 620 and the second conductive winding layer 655 form the windingfor the micromagnetic device.

An adhesive layer 660 (e.g., titanium) is formed above the secondconductive winding layer 655 in the center region of the substrate 605and over the fourth insulating layer 645 laterally beyond the centerregion of the substrate 605. Solder balls 665 are formed in apertures inthe adhesive layer 660.

Turning now to FIG. 20, illustrated is a partial cross-sectional view ofan embodiment of magnetic core layers of a magnetic core of amicromagnetic device employable in an integrated circuit constructedaccording to the principles of the present invention. While the presentembodiment illustrates two magnetic core layers, the micromagneticdevice may employ any number of magnetic core layers. The first andsecond magnetic core layers (designated “Layer 1” and “Layer 2”) includean adhesion layer (designated “Adhesive Layer”) of, without limitation,titanium or chromium and a seed layer (designed “Seed Layer”) of,without limitation, gold or copper. The first and second magnetic corelayers also include a magnetic core layer (designated “Magnetic CoreLayer”) of, without limitation, an iron-cobalt-phosphorus alloy and aprotective layer (designated “Protective Layer”) of, without limitation,nickel. First and second insulating layers (designated “Insulating Layer1” and “Insulating Layer 2”) include an adhesion layer (designated“Adhesive Layer”) of, without limitation, titanium or chromium and aninsulting layer (designated “Insulating Layer”) of, without limitation,silicon dioxide or aluminum oxide. The sequence of magnetic core layersand insulation layers can be repeated as needed to form the desirednumber of magnetic core layers.

Numerous variations of the micromagnetic device are possible includingadditional or alternative layers, and should be apparent to thoseskilled in the art. Additionally, for a more detailed analysis of themicromagnetic device as described above, see U.S. Pat. No. 7,544,995entitled “Power Converter Employing a Micromagnetic Device,” to Lotfi,et al, issued Jun. 9, 2009, which is incorporated herein by reference.For another example of a micromagnetic device, see U.S. Pat. No.6,495,019 entitled “Device Comprising Micromagnetic Components for PowerApplications and Process for Forming Device,” to Filas, et al., issuedDec. 17, 2002 and “Issues and Advances in High-Frequency Magnetics forSwitching Power Supplies,” by Lotfi, et al., Proceedings of the IEEE,Vol. 89, No. 6, pp. 833-845, June 2001, both of which are incorporatedherein by reference.

Turning now to FIG. 21, illustrate is a cross-sectional view of anembodiment of an output filter employable in an integrated circuitconstructed according to the principles of the present invention. In theillustrated embodiment, the output filter includes a capacitor coupledto an inductor embodied in a micromagnetic device. The output filter isconstructed on a semiconductor substrate (also referred to as a“substrate,” and composed of, for instance, silicon, glass, ceramic orthe like) 710 having a passivation layer (e.g., silicon dioxide) 720formed thereon using conventional formation processes such as a thermalgrowing process.

The micromagnetic device includes a first and second conductive windinglayer (composed of, for instance, aluminum or any other conductivematerial) 740, 760 surrounded by first, second and third insulatinglayers or insulators 730, 750, 770. The micromagnetic device alsoincludes a metallic layer 780 that provides an adequate bond between aferromagnetic core 790 and the insulators 730, 750, 770 coupled to thesubstrate 710 to facilitate the fabrication of the thereof. Themicromagnetic device still further includes a plurality of inner-layervias that provide multiple paths between layers of the micromagneticdevice and a terminal 796 for connection to another device.

The capacitor includes first and second capacitor plates 745, 755 and adielectric layer 735 located between the first and second capacitorplates 745, 755. The capacitor and micromagnetic device are electricallycoupled as illustrated by the conductive layers running therebetween.The capacitor also includes a plurality of inner-layer vias that providemultiple paths between the first and second plates 745, 755 of thecapacitor and a terminal 797 for connection to another device. Anembodiment of a micromagnetic device is disclosed in U.S. Pat. No.6,118,351 entitled “Micromagnetic Device for Power ProcessingApplications and Method of Manufacture Therefor,” to Kossives, et al.,issued Sep. 12, 2000, and several embodiments of filter circuits aredisclosed in U.S. Pat. No. 6,255,714 entitled “Integrated Circuit Havinga Micromagnetic Device Including a Ferromagnetic Core and Method ofManufacture Therefor,” to Kossives, et al., issued Jul. 3, 2001, both ofwhich are incorporated by reference.

Thus, a power converter embodied, or portions thereof, in an integratedcircuit and related methods of constructing the same with readilyattainable and quantifiable advantages has been introduced. Thoseskilled in the art should understand that the previously describedembodiments of the integrated circuit including the power converter andportions thereof embodied in the integrated circuit and related methodsof constructing the same are submitted for illustrative purposes only.In addition, other embodiments capable of producing an integratedcircuit employable with higher voltage devices and low voltage devicesintegrable within a semiconductor device are well within the broad scopeof the present invention. While the integrated circuit has beendescribed in the environment of a power converter, the integratedcircuit may also apply to other systems such as a power amplifier, motorcontroller, and a system to control an actuator in accordance with astepper motor or other electromechanical device.

In one embodiment, the integrated circuit includes a transistoradvantageously embodied in a LDMOS device having a gate located over achannel region recessed into a semiconductor substrate. The transistorincludes a source/drain including a lightly doped region adjacent thechannel region and a heavily doped region adjacent but not surrounded bythe lightly doped region. An isolation region of the transistor isadjacent the heavily doped region opposite the lightly doped region. Thetransistor also includes an oppositely doped well extending under thechannel region and a portion of the lightly doped region of thesource/drain. The transistor also includes a channel extension, withinthe oppositely doped well, under the channel region and extending undera portion of the lightly doped region of the source/drain by a channelextension length. The channel extension is typically of like type to andhas a doping concentration profile greater than a doping concentrationprofile of the oppositely doped well. The transistor also includes adoped region adjacent the oppositely doped well and extending under aportion of the lightly doped region of the source/drain, and anoppositely doped buried layer under the doped region. The transistoralso includes another source/drain having a lightly or heavily dopedregion adjacent an opposing side of the channel region, wherein thechannel extension extends under a portion of the lightly or heavilydoped region of the another source/drain by a channel extension length.The transistor also includes a gate dielectric layer underlying thegate, gate sidewall spacers formed about the gate, and metal contactsformed over a salicide layer formed on the gate and the source/drain.

For a related integrated circuit, see U.S. Pat. No. 7,214,985 entitled“Integrated Circuit Incorporating Higher Voltage Devices and Low VoltageDevices Therein,” to Lotfi, et al., issued May 8, 2007, which isincorporated herein by reference. For a better understanding ofintegrated circuits, semiconductor devices and methods of manufacturetherefor see “Semiconductor Device Fundamentals,” by R. F. Pierret,Addison-Wesley (1996); “Handbook of Sputter Deposition Technology,” byK. Wasa and S. Hayakawa, Noyes Publications (1992); “Thin FilmTechnology,” by R. W. Berry, P. M. Hall and M. T. Harris, Van Nostrand(1968); “Thin Film Processes,” by J. Vossen and W. Kern, Academic(1978); and “Handbook of Thin Film Technology,” by L. Maissel and R.Glang, McGraw Hill (1970). For a better understanding of powerconverters, see “Modern DC-to-DC Switchmode Power Converter Circuits,”by Rudolph P. Severns and Gordon Bloom, Van Nostrand Reinhold Company,New York, N.Y. (1985) and “Principles of Power Electronics,” by J. G.Kassakian, M. F. Schlecht and G. C. Verghese, Addison-Wesley (1991). Theaforementioned references are incorporated herein by reference in theirentirety.

Also, although the present invention and its advantages have beendescribed in detail, it should be understood that various changes,substitutions and alterations can be made herein without departing fromthe spirit and scope of the invention as defined by the appended claims.For example, many of the processes discussed above can be implemented indifferent methodologies and replaced by other processes, or acombination thereof.

Moreover, the scope of the present application is not intended to belimited to the particular embodiments of the process, machine,manufacture, composition of matter, means, methods and steps describedin the specification. As one of ordinary skill in the art will readilyappreciate from the disclosure of the present invention, processes,machines, manufacture, compositions of matter, means, methods, or steps,presently existing or later to be developed, that perform substantiallythe same function or achieve substantially the same result as thecorresponding embodiments described herein may be utilized according tothe present invention. Accordingly, the appended claims are intended toinclude within their scope such processes, machines, manufacture,compositions of matter, means, methods, or steps.

1. An integrated circuit on a semiconductor substrate, comprising: atransistor, including: a gate located over a channel region recessedinto said semiconductor substrate, a source/drain including a lightlydoped region adjacent said channel region, an oppositely doped wellextending under said channel region and a portion of said lightly dopedregion of said source/drain, a doped region adjacent said oppositelydoped well and extending under a portion of said lightly doped region ofsaid source/drain; an oppositely doped buried layer under said dopedregion; and a channel extension, within said oppositely doped well,under said channel region and extending under a portion of said lightlydoped region of said source/drain; and a driver switch of a driverformed on said semiconductor substrate and configured to provide a drivesignal to said transistor.
 2. The integrated circuit as recited in claim1 wherein said channel extension extends under said portion of saidlightly doped region of said source/drain by a channel extension length.3. The integrated circuit as recited in claim 1 wherein said channelextension is of like type to and has a doping concentration profilegreater than a doping concentration profile of said oppositely dopedwell.
 4. The integrated circuit as recited in claim 1 wherein saidsource/drain includes a heavily doped region adjacent said lightly dopedregion of said source/drain.
 5. The integrated circuit as recited inclaim 1 wherein said source/drain includes a heavily doped regionadjacent but not surrounded by said lightly doped region of saidsource/drain.
 6. The integrated circuit as recited in claim 1 whereinsaid source/drain includes a heavily doped region adjacent said lightlydoped region, said transistor further comprising an isolation regionadjacent said heavily doped region of said source/drain.
 7. Theintegrated circuit as recited in claim 1 wherein said transistor furthercomprises another source/drain having a lightly doped region adjacent anopposing side of said channel region, said channel extension extendingunder a portion of said lightly doped region of said anothersource/drain by a channel extension length.
 8. The integrated circuit asrecited in claim 1 wherein said transistor further comprises anothersource/drain having a heavily doped region adjacent an opposing side ofsaid channel region, said channel extension extending under a portion ofsaid heavily doped region of said another source/drain by a channelextension length.
 9. The integrated circuit as recited in claim 1wherein said channel extension extends under only a portion of saidlightly doped region of said source/drain.
 10. The integrated circuit asrecited in claim 1 wherein said transistor further comprises a gatedielectric layer underlying said gate and gate sidewall spacers formedabout said gate, said transistor further comprising metal contactsformed over a salicide layer formed on said gate and said source/drain.11. The integrated circuit as recited in claim 1 wherein said oppositelydoped buried layer has a doping concentration profile in a range of1·10¹⁸ to 1·10²⁰ atoms/centimeter³.
 12. The integrated circuit asrecited in claim 1 wherein said oppositely doped well has a retrogradedoping concentration profile with about 1·10¹⁷ atoms/centimeter³ in amiddle area thereof.
 13. The integrated circuit as recited in claim 1wherein said oppositely doped well has a retrograde doping concentrationprofile with higher doping concentration profile at a top surfacecompared to a middle area thereof.
 14. The integrated circuit as recitedin claim 1 wherein said channel extension has a doping concentrationprofile of about 1.2·10¹⁸ atoms/centimeter³.
 15. The integrated circuitas recited in claim 1 wherein said lightly doped region of saidsource/drain has a doping concentration profile in a range of 1·10¹⁶ to1·10¹⁷ atoms/centimeter³.
 16. The integrated circuit as recited in claim1 wherein said gate has a thickness in a range from about 100 to 500nanometers.
 17. The integrated circuit as recited in claim 1 whereinsaid doped region has a doping concentration profile in a range of1·10¹⁴ to 1·10¹⁶ atoms/centimeter³.
 18. The integrated circuit asrecited in claim 1 wherein said channel extension extends under saidportion of said lightly doped region of said source/drain by a channelextension length, said channel extension length being selected toprovide an increased breakdown voltage and reduced on-state resistancefor said laterally diffused metal oxide semiconductor device.
 19. Theintegrated circuit as recited in claim 1 wherein said channel extensionextends under said portion of said lightly doped region of saidsource/drain by about 0.3 micrometers, a channel extension dose is about1·10¹³ centimeters⁻², a channel extension energy is about 160 kilovolts,and a length and dose of said lightly doped region of said source drainis about 0.6 micrometers and 5·10¹² centimeters⁻², respectively.
 20. Theintegrated circuit as recited in claim 1 wherein lightly doped region ofsaid source/drain and said doped region are P-type, and said oppositelydoped well, channel extension and oppositely doped buried layer areN-type.